diff --git a/BUILD b/BUILD
index 506abaa..7c7f9e0 100644
--- a/BUILD
+++ b/BUILD
@@ -20,6 +20,7 @@
         "Gerrit-PluginName: code-owners",
         "Gerrit-Module: com.google.gerrit.plugins.codeowners.module.Module",
         "Gerrit-HttpModule: com.google.gerrit.plugins.codeowners.module.HttpModule",
+        "Gerrit-BatchModule: com.google.gerrit.plugins.codeowners.module.BatchModule",
     ],
     resource_jars = [":code-owners-fe-static"],
     resource_strip_prefix = "plugins/code-owners/resources",
diff --git a/java/com/google/gerrit/plugins/codeowners/acceptance/AbstractCodeOwnersIT.java b/java/com/google/gerrit/plugins/codeowners/acceptance/AbstractCodeOwnersIT.java
index 0b50f6e..26578fc 100644
--- a/java/com/google/gerrit/plugins/codeowners/acceptance/AbstractCodeOwnersIT.java
+++ b/java/com/google/gerrit/plugins/codeowners/acceptance/AbstractCodeOwnersIT.java
@@ -15,6 +15,7 @@
 package com.google.gerrit.plugins.codeowners.acceptance;
 
 import static com.google.common.collect.ImmutableMap.toImmutableMap;
+import static com.google.common.truth.TruthJUnit.assume;
 
 import com.google.common.collect.ImmutableMap;
 import com.google.gerrit.plugins.codeowners.acceptance.testsuite.CodeOwnerConfigOperations;
@@ -24,6 +25,7 @@
 import com.google.gerrit.plugins.codeowners.api.impl.ProjectCodeOwnersFactory;
 import com.google.gerrit.plugins.codeowners.backend.CodeOwnerBackendId;
 import com.google.gerrit.plugins.codeowners.backend.config.BackendConfig;
+import com.google.gerrit.plugins.codeowners.backend.proto.ProtoBackend;
 import com.google.gerrit.testing.ConfigSuite;
 import java.util.Arrays;
 import org.eclipse.jgit.lib.Config;
@@ -76,6 +78,8 @@
   protected ChangeCodeOwnersFactory changeCodeOwnersApiFactory;
   protected ProjectCodeOwnersFactory projectCodeOwnersApiFactory;
 
+  private BackendConfig backendConfig;
+
   @Before
   public void baseSetup() throws Exception {
     codeOwnerConfigOperations =
@@ -85,5 +89,15 @@
     changeCodeOwnersApiFactory = plugin.getSysInjector().getInstance(ChangeCodeOwnersFactory.class);
     projectCodeOwnersApiFactory =
         plugin.getSysInjector().getInstance(ProjectCodeOwnersFactory.class);
+    backendConfig = plugin.getSysInjector().getInstance(BackendConfig.class);
+  }
+
+  protected void skipTestIfImportsNotSupportedByCodeOwnersBackend() {
+    // the proto backend doesn't support imports
+    assumeThatCodeOwnersBackendIsNotProtoBackend();
+  }
+
+  protected void assumeThatCodeOwnersBackendIsNotProtoBackend() {
+    assume().that(backendConfig.getDefaultBackend()).isNotInstanceOf(ProtoBackend.class);
   }
 }
diff --git a/java/com/google/gerrit/plugins/codeowners/api/impl/BranchCodeOwnersImpl.java b/java/com/google/gerrit/plugins/codeowners/api/impl/BranchCodeOwnersImpl.java
index 81a418c..231d591 100644
--- a/java/com/google/gerrit/plugins/codeowners/api/impl/BranchCodeOwnersImpl.java
+++ b/java/com/google/gerrit/plugins/codeowners/api/impl/BranchCodeOwnersImpl.java
@@ -18,8 +18,6 @@
 
 import com.google.gerrit.extensions.restapi.RestApiException;
 import com.google.gerrit.plugins.codeowners.api.BranchCodeOwners;
-import com.google.gerrit.plugins.codeowners.api.BranchCodeOwners.CodeOwnerCheckRequest;
-import com.google.gerrit.plugins.codeowners.api.BranchCodeOwners.CodeOwnerConfigFilesRequest;
 import com.google.gerrit.plugins.codeowners.api.CodeOwnerBranchConfigInfo;
 import com.google.gerrit.plugins.codeowners.api.CodeOwnerCheckInfo;
 import com.google.gerrit.plugins.codeowners.api.RenameEmailInput;
diff --git a/java/com/google/gerrit/plugins/codeowners/api/impl/CodeOwnersInBranchImpl.java b/java/com/google/gerrit/plugins/codeowners/api/impl/CodeOwnersInBranchImpl.java
index f9e3fdf..fab0648 100644
--- a/java/com/google/gerrit/plugins/codeowners/api/impl/CodeOwnersInBranchImpl.java
+++ b/java/com/google/gerrit/plugins/codeowners/api/impl/CodeOwnersInBranchImpl.java
@@ -20,7 +20,6 @@
 import com.google.gerrit.extensions.restapi.RestApiException;
 import com.google.gerrit.plugins.codeowners.api.CodeOwnerInfo;
 import com.google.gerrit.plugins.codeowners.api.CodeOwners;
-import com.google.gerrit.plugins.codeowners.api.CodeOwners.QueryRequest;
 import com.google.gerrit.plugins.codeowners.restapi.CodeOwnersInBranchCollection;
 import com.google.gerrit.plugins.codeowners.restapi.GetCodeOwnersForPathInBranch;
 import com.google.gerrit.server.project.BranchResource;
diff --git a/java/com/google/gerrit/plugins/codeowners/api/impl/CodeOwnersInChangeImpl.java b/java/com/google/gerrit/plugins/codeowners/api/impl/CodeOwnersInChangeImpl.java
index d1281fd..f91c08f 100644
--- a/java/com/google/gerrit/plugins/codeowners/api/impl/CodeOwnersInChangeImpl.java
+++ b/java/com/google/gerrit/plugins/codeowners/api/impl/CodeOwnersInChangeImpl.java
@@ -21,7 +21,6 @@
 import com.google.gerrit.extensions.restapi.RestApiException;
 import com.google.gerrit.plugins.codeowners.api.CodeOwnerInfo;
 import com.google.gerrit.plugins.codeowners.api.CodeOwners;
-import com.google.gerrit.plugins.codeowners.api.CodeOwners.QueryRequest;
 import com.google.gerrit.plugins.codeowners.restapi.CodeOwnersInChangeCollection;
 import com.google.gerrit.plugins.codeowners.restapi.GetCodeOwnersForPathInChange;
 import com.google.gerrit.server.change.RevisionResource;
diff --git a/java/com/google/gerrit/plugins/codeowners/api/impl/ProjectCodeOwnersImpl.java b/java/com/google/gerrit/plugins/codeowners/api/impl/ProjectCodeOwnersImpl.java
index 7d578e5..2085640 100644
--- a/java/com/google/gerrit/plugins/codeowners/api/impl/ProjectCodeOwnersImpl.java
+++ b/java/com/google/gerrit/plugins/codeowners/api/impl/ProjectCodeOwnersImpl.java
@@ -23,7 +23,6 @@
 import com.google.gerrit.plugins.codeowners.api.CheckCodeOwnerConfigFilesInput;
 import com.google.gerrit.plugins.codeowners.api.CodeOwnerProjectConfigInfo;
 import com.google.gerrit.plugins.codeowners.api.ProjectCodeOwners;
-import com.google.gerrit.plugins.codeowners.api.ProjectCodeOwners.CheckCodeOwnerConfigFilesRequest;
 import com.google.gerrit.plugins.codeowners.restapi.CheckCodeOwnerConfigFiles;
 import com.google.gerrit.plugins.codeowners.restapi.GetCodeOwnerProjectConfig;
 import com.google.gerrit.server.project.BranchResource;
diff --git a/java/com/google/gerrit/plugins/codeowners/api/impl/RevisionCodeOwnersImpl.java b/java/com/google/gerrit/plugins/codeowners/api/impl/RevisionCodeOwnersImpl.java
index a4ea2bd..11ab392 100644
--- a/java/com/google/gerrit/plugins/codeowners/api/impl/RevisionCodeOwnersImpl.java
+++ b/java/com/google/gerrit/plugins/codeowners/api/impl/RevisionCodeOwnersImpl.java
@@ -20,7 +20,6 @@
 import com.google.gerrit.extensions.restapi.RestApiException;
 import com.google.gerrit.plugins.codeowners.api.CheckCodeOwnerConfigFilesInRevisionInput;
 import com.google.gerrit.plugins.codeowners.api.RevisionCodeOwners;
-import com.google.gerrit.plugins.codeowners.api.RevisionCodeOwners.CheckCodeOwnerConfigFilesRequest;
 import com.google.gerrit.plugins.codeowners.restapi.CheckCodeOwnerConfigFilesInRevision;
 import com.google.gerrit.server.change.RevisionResource;
 import com.google.inject.Inject;
diff --git a/java/com/google/gerrit/plugins/codeowners/backend/CodeOwnersExceptionHook.java b/java/com/google/gerrit/plugins/codeowners/backend/CodeOwnersExceptionHook.java
index 53d7cd2..8a2e85e 100644
--- a/java/com/google/gerrit/plugins/codeowners/backend/CodeOwnersExceptionHook.java
+++ b/java/com/google/gerrit/plugins/codeowners/backend/CodeOwnersExceptionHook.java
@@ -19,6 +19,7 @@
 import com.google.gerrit.common.Nullable;
 import com.google.gerrit.plugins.codeowners.backend.config.InvalidPluginConfigurationException;
 import com.google.gerrit.server.ExceptionHook;
+import java.nio.file.InvalidPathException;
 import java.util.Optional;
 import org.eclipse.jgit.errors.ConfigInvalidException;
 
@@ -39,7 +40,8 @@
   @Override
   public boolean skipRetryWithTrace(String actionType, String actionName, Throwable throwable) {
     return isInvalidPluginConfigurationException(throwable)
-        || isInvalidCodeOwnerConfigException(throwable);
+        || isInvalidCodeOwnerConfigException(throwable)
+        || isInvalidPathException(throwable);
   }
 
   @Override
@@ -56,13 +58,19 @@
       return ImmutableList.of(configInvalidException.get().getMessage());
     }
 
+    Optional<InvalidPathException> invalidPathException = getInvalidPathException(throwable);
+    if (invalidPathException.isPresent()) {
+      return ImmutableList.of(invalidPathException.get().getMessage());
+    }
+
     return ImmutableList.of();
   }
 
   @Override
   public Optional<Status> getStatus(Throwable throwable) {
     if (isInvalidPluginConfigurationException(throwable)
-        || isInvalidCodeOwnerConfigException(throwable)) {
+        || isInvalidCodeOwnerConfigException(throwable)
+        || isInvalidPathException(throwable)) {
       return Optional.of(Status.create(409, "Conflict"));
     }
     return Optional.empty();
@@ -74,9 +82,22 @@
 
   private static Optional<InvalidPluginConfigurationException> getInvalidPluginConfigurationCause(
       Throwable throwable) {
+    return getInvalidPluginConfigurationCause(InvalidPluginConfigurationException.class, throwable);
+  }
+
+  private static boolean isInvalidPathException(Throwable throwable) {
+    return getInvalidPathException(throwable).isPresent();
+  }
+
+  private static Optional<InvalidPathException> getInvalidPathException(Throwable throwable) {
+    return getInvalidPluginConfigurationCause(InvalidPathException.class, throwable);
+  }
+
+  private static <T extends Throwable> Optional<T> getInvalidPluginConfigurationCause(
+      Class<T> exceptionClass, Throwable throwable) {
     return Throwables.getCausalChain(throwable).stream()
-        .filter(t -> t instanceof InvalidPluginConfigurationException)
-        .map(t -> (InvalidPluginConfigurationException) t)
+        .filter(exceptionClass::isInstance)
+        .map(exceptionClass::cast)
         .findFirst();
   }
 
diff --git a/javatests/com/google/gerrit/plugins/codeowners/acceptance/api/CheckCodeOwnerConfigFilesIT.java b/javatests/com/google/gerrit/plugins/codeowners/acceptance/api/CheckCodeOwnerConfigFilesIT.java
index 758d0ef..a2e37ef 100644
--- a/javatests/com/google/gerrit/plugins/codeowners/acceptance/api/CheckCodeOwnerConfigFilesIT.java
+++ b/javatests/com/google/gerrit/plugins/codeowners/acceptance/api/CheckCodeOwnerConfigFilesIT.java
@@ -15,7 +15,6 @@
 package com.google.gerrit.plugins.codeowners.acceptance.api;
 
 import static com.google.common.truth.Truth.assertThat;
-import static com.google.common.truth.TruthJUnit.assume;
 import static com.google.gerrit.acceptance.testsuite.project.TestProjectUpdate.block;
 import static com.google.gerrit.server.group.SystemGroupBackend.REGISTERED_USERS;
 import static com.google.gerrit.testing.GerritJUnit.assertThrows;
@@ -196,8 +195,7 @@
 
   private void testIssuesInCodeOwnerConfigFile(ConsistencyProblemInfo.Status expectedStatus)
       throws Exception {
-    // imports are not supported for the proto backend
-    assume().that(backendConfig.getDefaultBackend()).isNotInstanceOf(ProtoBackend.class);
+    skipTestIfImportsNotSupportedByCodeOwnersBackend();
 
     // Create some code owner config files with issues.
     CodeOwnerConfig.Key keyOfInvalidConfig1 =
@@ -393,8 +391,7 @@
 
   @Test
   public void validateExactFile() throws Exception {
-    // imports are not supported for the proto backend
-    assume().that(backendConfig.getDefaultBackend()).isNotInstanceOf(ProtoBackend.class);
+    skipTestIfImportsNotSupportedByCodeOwnersBackend();
 
     // Create some code owner config files with issues.
     CodeOwnerConfig.Key keyOfInvalidConfig1 =
@@ -466,8 +463,7 @@
 
   @Test
   public void validateFilesMatchingGlob() throws Exception {
-    // imports are not supported for the proto backend
-    assume().that(backendConfig.getDefaultBackend()).isNotInstanceOf(ProtoBackend.class);
+    skipTestIfImportsNotSupportedByCodeOwnersBackend();
 
     // Create some code owner config files with issues.
     codeOwnerConfigOperations
diff --git a/javatests/com/google/gerrit/plugins/codeowners/acceptance/api/CheckCodeOwnerIT.java b/javatests/com/google/gerrit/plugins/codeowners/acceptance/api/CheckCodeOwnerIT.java
index 282594b..8166970 100644
--- a/javatests/com/google/gerrit/plugins/codeowners/acceptance/api/CheckCodeOwnerIT.java
+++ b/javatests/com/google/gerrit/plugins/codeowners/acceptance/api/CheckCodeOwnerIT.java
@@ -15,7 +15,6 @@
 package com.google.gerrit.plugins.codeowners.acceptance.api;
 
 import static com.google.common.truth.Truth.assertThat;
-import static com.google.common.truth.TruthJUnit.assume;
 import static com.google.gerrit.acceptance.testsuite.project.TestProjectUpdate.allowCapability;
 import static com.google.gerrit.plugins.codeowners.testing.CodeOwnerCheckInfoSubject.assertThat;
 import static com.google.gerrit.server.group.SystemGroupBackend.REGISTERED_USERS;
@@ -612,8 +611,7 @@
 
   @Test
   public void debugLogsContainUnresolvedImports() throws Exception {
-    // imports are not supported for the proto backend
-    assume().that(backendConfig.getDefaultBackend()).isNotInstanceOf(ProtoBackend.class);
+    skipTestIfImportsNotSupportedByCodeOwnersBackend();
 
     CodeOwnerConfigReference unresolvableCodeOwnerConfigReference =
         CodeOwnerConfigReference.create(
diff --git a/javatests/com/google/gerrit/plugins/codeowners/acceptance/api/CodeOwnerConfigValidatorIT.java b/javatests/com/google/gerrit/plugins/codeowners/acceptance/api/CodeOwnerConfigValidatorIT.java
index e65efbd..12b3360 100644
--- a/javatests/com/google/gerrit/plugins/codeowners/acceptance/api/CodeOwnerConfigValidatorIT.java
+++ b/javatests/com/google/gerrit/plugins/codeowners/acceptance/api/CodeOwnerConfigValidatorIT.java
@@ -15,7 +15,6 @@
 package com.google.gerrit.plugins.codeowners.acceptance.api;
 
 import static com.google.common.truth.Truth.assertThat;
-import static com.google.common.truth.TruthJUnit.assume;
 import static com.google.gerrit.acceptance.testsuite.project.TestProjectUpdate.allow;
 import static com.google.gerrit.acceptance.testsuite.project.TestProjectUpdate.block;
 import static com.google.gerrit.server.group.SystemGroupBackend.REGISTERED_USERS;
@@ -152,8 +151,7 @@
 
   @Test
   public void canUploadConfigWithoutIssues_withImport() throws Exception {
-    // imports are not supported for the proto backend
-    assume().that(backendConfig.getDefaultBackend()).isNotInstanceOf(ProtoBackend.class);
+    skipTestIfImportsNotSupportedByCodeOwnersBackend();
 
     CodeOwnerConfig.Key codeOwnerConfigKey = createCodeOwnerConfigKey("/");
 
@@ -198,8 +196,7 @@
 
   @Test
   public void canUploadConfigWithoutIssues_withImportFromOtherProject() throws Exception {
-    // imports are not supported for the proto backend
-    assume().that(backendConfig.getDefaultBackend()).isNotInstanceOf(ProtoBackend.class);
+    skipTestIfImportsNotSupportedByCodeOwnersBackend();
 
     CodeOwnerConfig.Key codeOwnerConfigKey = createCodeOwnerConfigKey("/");
 
@@ -243,8 +240,7 @@
 
   @Test
   public void canUploadConfigWithoutIssues_withImportFromOtherProjectAndBranch() throws Exception {
-    // imports are not supported for the proto backend
-    assume().that(backendConfig.getDefaultBackend()).isNotInstanceOf(ProtoBackend.class);
+    skipTestIfImportsNotSupportedByCodeOwnersBackend();
 
     CodeOwnerConfig.Key codeOwnerConfigKey = createCodeOwnerConfigKey("/");
 
@@ -292,8 +288,7 @@
   public void
       canUploadConfigWithImportOfConfigThatIsAddedInSameCommit_importModeGlobalCodeOwnersOnly()
           throws Exception {
-    // imports are not supported for the proto backend
-    assume().that(backendConfig.getDefaultBackend()).isNotInstanceOf(ProtoBackend.class);
+    skipTestIfImportsNotSupportedByCodeOwnersBackend();
 
     CodeOwnerConfig.Key codeOwnerConfigKey = createCodeOwnerConfigKey("/");
     CodeOwnerConfig.Key keyOfImportedCodeOwnerConfig = createCodeOwnerConfigKey("/foo/");
@@ -332,8 +327,7 @@
   @Test
   public void canUploadConfigWithImportOfConfigThatIsAddedInSameCommit_importModeAll()
       throws Exception {
-    // imports are not supported for the proto backend
-    assume().that(backendConfig.getDefaultBackend()).isNotInstanceOf(ProtoBackend.class);
+    skipTestIfImportsNotSupportedByCodeOwnersBackend();
 
     CodeOwnerConfig.Key codeOwnerConfigKey = createCodeOwnerConfigKey("/");
     CodeOwnerConfig.Key keyOfImportedCodeOwnerConfig = createCodeOwnerConfigKey("/foo/");
@@ -1040,8 +1034,7 @@
 
   private void testUploadConfigWithImportFromNonExistingProject(
       CodeOwnerConfigImportType importType) throws Exception {
-    // imports are not supported for the proto backend
-    assume().that(backendConfig.getDefaultBackend()).isNotInstanceOf(ProtoBackend.class);
+    skipTestIfImportsNotSupportedByCodeOwnersBackend();
 
     // create a code owner config that imports a code owner config from a non-existing project
     CodeOwnerConfig.Key keyOfImportingCodeOwnerConfig = createCodeOwnerConfigKey("/");
@@ -1087,8 +1080,7 @@
 
   private void testUploadConfigWithImportFromNonVisibleProject(CodeOwnerConfigImportType importType)
       throws Exception {
-    // imports are not supported for the proto backend
-    assume().that(backendConfig.getDefaultBackend()).isNotInstanceOf(ProtoBackend.class);
+    skipTestIfImportsNotSupportedByCodeOwnersBackend();
 
     // create a non-visible project with a code owner config file that we try to import
     Project.NameKey nonVisibleProject =
@@ -1150,8 +1142,7 @@
 
   private void testUploadConfigWithImportFromHiddenProject(CodeOwnerConfigImportType importType)
       throws Exception {
-    // imports are not supported for the proto backend
-    assume().that(backendConfig.getDefaultBackend()).isNotInstanceOf(ProtoBackend.class);
+    skipTestIfImportsNotSupportedByCodeOwnersBackend();
 
     // create a hidden project with a code owner config file
     Project.NameKey hiddenProject =
@@ -1210,8 +1201,7 @@
 
   private void testUploadConfigWithImportFromNonExistingBranch(CodeOwnerConfigImportType importType)
       throws Exception {
-    // imports are not supported for the proto backend
-    assume().that(backendConfig.getDefaultBackend()).isNotInstanceOf(ProtoBackend.class);
+    skipTestIfImportsNotSupportedByCodeOwnersBackend();
 
     // create a code owner config that imports a code owner config from a non-existing branch
     CodeOwnerConfig.Key keyOfImportingCodeOwnerConfig = createCodeOwnerConfigKey("/");
@@ -1258,8 +1248,7 @@
 
   private void testUploadConfigWithImportFromNonVisibleBranch(CodeOwnerConfigImportType importType)
       throws Exception {
-    // imports are not supported for the proto backend
-    assume().that(backendConfig.getDefaultBackend()).isNotInstanceOf(ProtoBackend.class);
+    skipTestIfImportsNotSupportedByCodeOwnersBackend();
 
     CodeOwnerConfig.Key keyOfImportingCodeOwnerConfig = createCodeOwnerConfigKey("/");
 
@@ -1323,8 +1312,7 @@
 
   private void testUploadConfigWithImportOfNonCodeOwnerConfigFile(
       CodeOwnerConfigImportType importType) throws Exception {
-    // imports are not supported for the proto backend
-    assume().that(backendConfig.getDefaultBackend()).isNotInstanceOf(ProtoBackend.class);
+    skipTestIfImportsNotSupportedByCodeOwnersBackend();
 
     // create a code owner config that imports a non code owner config file
     CodeOwnerConfig.Key keyOfImportingCodeOwnerConfig = createCodeOwnerConfigKey("/");
@@ -1368,8 +1356,7 @@
 
   private void testUploadConfigWithImportOfNonExistingCodeOwnerConfig(
       CodeOwnerConfigImportType importType) throws Exception {
-    // imports are not supported for the proto backend
-    assume().that(backendConfig.getDefaultBackend()).isNotInstanceOf(ProtoBackend.class);
+    skipTestIfImportsNotSupportedByCodeOwnersBackend();
 
     // create a code owner config that imports a non-existing code owner config
     CodeOwnerConfig.Key keyOfImportingCodeOwnerConfig = createCodeOwnerConfigKey("/");
@@ -1421,8 +1408,7 @@
 
   private void testUploadConfigWithImportOfNonParseableCodeOwnerConfig(
       CodeOwnerConfigImportType importType) throws Exception {
-    // imports are not supported for the proto backend
-    assume().that(backendConfig.getDefaultBackend()).isNotInstanceOf(ProtoBackend.class);
+    skipTestIfImportsNotSupportedByCodeOwnersBackend();
 
     CodeOwnerConfig.Key keyOfImportedCodeOwnerConfig =
         CodeOwnerConfig.Key.create(project, "master", "/foo/");
@@ -1629,8 +1615,7 @@
   @Test
   @GerritConfig(name = "plugin.code-owners.rejectNonResolvableImports", value = "false")
   public void canUploadAndSubmitConfigWithUnresolvableImports() throws Exception {
-    // imports are not supported for the proto backend
-    assume().that(backendConfig.getDefaultBackend()).isNotInstanceOf(ProtoBackend.class);
+    skipTestIfImportsNotSupportedByCodeOwnersBackend();
 
     CodeOwnerConfig.Key keyOfImportingCodeOwnerConfig = createCodeOwnerConfigKey("/");
 
@@ -1685,8 +1670,7 @@
   @GerritConfig(name = "plugin.code-owners.enableValidationOnCommitReceived", value = "false")
   @GerritConfig(name = "plugin.code-owners.enableValidationOnSubmit", value = "false")
   public void rejectConfigOptionsAreIgnoredIfValidationIsDisabled() throws Exception {
-    // imports are not supported for the proto backend
-    assume().that(backendConfig.getDefaultBackend()).isNotInstanceOf(ProtoBackend.class);
+    skipTestIfImportsNotSupportedByCodeOwnersBackend();
 
     CodeOwnerConfig.Key keyOfImportingCodeOwnerConfig = createCodeOwnerConfigKey("/");
 
diff --git a/javatests/com/google/gerrit/plugins/codeowners/acceptance/api/RenameEmailIT.java b/javatests/com/google/gerrit/plugins/codeowners/acceptance/api/RenameEmailIT.java
index 40d87a6..463d623 100644
--- a/javatests/com/google/gerrit/plugins/codeowners/acceptance/api/RenameEmailIT.java
+++ b/javatests/com/google/gerrit/plugins/codeowners/acceptance/api/RenameEmailIT.java
@@ -15,7 +15,6 @@
 package com.google.gerrit.plugins.codeowners.acceptance.api;
 
 import static com.google.common.truth.Truth.assertThat;
-import static com.google.common.truth.TruthJUnit.assume;
 import static com.google.gerrit.acceptance.testsuite.project.TestProjectUpdate.allow;
 import static com.google.gerrit.acceptance.testsuite.project.TestProjectUpdate.allowCapability;
 import static com.google.gerrit.plugins.codeowners.testing.CodeOwnerConfigSubject.assertThat;
@@ -41,8 +40,6 @@
 import com.google.gerrit.plugins.codeowners.api.RenameEmailResultInfo;
 import com.google.gerrit.plugins.codeowners.backend.CodeOwnerConfig;
 import com.google.gerrit.plugins.codeowners.backend.CodeOwnerConfigFileUpdateScanner;
-import com.google.gerrit.plugins.codeowners.backend.config.BackendConfig;
-import com.google.gerrit.plugins.codeowners.backend.proto.ProtoBackend;
 import com.google.gerrit.plugins.codeowners.restapi.RenameEmail;
 import com.google.inject.Inject;
 import java.util.Optional;
@@ -62,12 +59,10 @@
   @Inject private ProjectOperations projectOperations;
   @Inject private RequestScopeOperations requestScopeOperations;
 
-  private BackendConfig backendConfig;
   private CodeOwnerConfigFileUpdateScanner codeOwnerConfigFileUpdateScanner;
 
   @Before
   public void setup() throws Exception {
-    backendConfig = plugin.getSysInjector().getInstance(BackendConfig.class);
     codeOwnerConfigFileUpdateScanner =
         plugin.getSysInjector().getInstance(CodeOwnerConfigFileUpdateScanner.class);
   }
@@ -179,8 +174,7 @@
 
   @Test
   public void renameEmail_noUpdateIfEmailIsNotContainedInCodeOwnerConfigs() throws Exception {
-    // renaming email is not supported for the proto backend
-    assume().that(backendConfig.getDefaultBackend()).isNotInstanceOf(ProtoBackend.class);
+    skipTestIfRenameEmailNotSupportedByCodeOwnersBackend();
 
     codeOwnerConfigOperations
         .newCodeOwnerConfig()
@@ -210,8 +204,7 @@
 
   @Test
   public void renameOwnEmailWithDirectPushPermission() throws Exception {
-    // renaming email is not supported for the proto backend
-    assume().that(backendConfig.getDefaultBackend()).isNotInstanceOf(ProtoBackend.class);
+    skipTestIfRenameEmailNotSupportedByCodeOwnersBackend();
 
     CodeOwnerConfig.Key codeOwnerConfigKey1 =
         codeOwnerConfigOperations
@@ -263,8 +256,7 @@
 
   @Test
   public void renameOtherEmailWithDirectPushPermission() throws Exception {
-    // renaming email is not supported for the proto backend
-    assume().that(backendConfig.getDefaultBackend()).isNotInstanceOf(ProtoBackend.class);
+    skipTestIfRenameEmailNotSupportedByCodeOwnersBackend();
 
     CodeOwnerConfig.Key codeOwnerConfigKey1 =
         codeOwnerConfigOperations
@@ -323,8 +315,7 @@
 
   @Test
   public void renameOwnEmailAsProjectOwner() throws Exception {
-    // renaming email is not supported for the proto backend
-    assume().that(backendConfig.getDefaultBackend()).isNotInstanceOf(ProtoBackend.class);
+    skipTestIfRenameEmailNotSupportedByCodeOwnersBackend();
 
     CodeOwnerConfig.Key codeOwnerConfigKey1 =
         codeOwnerConfigOperations
@@ -368,8 +359,7 @@
 
   @Test
   public void renameOtherEmailAsProjectOwner() throws Exception {
-    // renaming email is not supported for the proto backend
-    assume().that(backendConfig.getDefaultBackend()).isNotInstanceOf(ProtoBackend.class);
+    skipTestIfRenameEmailNotSupportedByCodeOwnersBackend();
 
     CodeOwnerConfig.Key codeOwnerConfigKey1 =
         codeOwnerConfigOperations
@@ -413,8 +403,7 @@
 
   @Test
   public void renameEmail_callingUserBecomesCommitAuthor() throws Exception {
-    // renaming email is not supported for the proto backend
-    assume().that(backendConfig.getDefaultBackend()).isNotInstanceOf(ProtoBackend.class);
+    skipTestIfRenameEmailNotSupportedByCodeOwnersBackend();
 
     codeOwnerConfigOperations
         .newCodeOwnerConfig()
@@ -438,8 +427,7 @@
 
   @Test
   public void renameEmailWithDefaultCommitMessage() throws Exception {
-    // renaming email is not supported for the proto backend
-    assume().that(backendConfig.getDefaultBackend()).isNotInstanceOf(ProtoBackend.class);
+    skipTestIfRenameEmailNotSupportedByCodeOwnersBackend();
 
     codeOwnerConfigOperations
         .newCodeOwnerConfig()
@@ -463,8 +451,7 @@
 
   @Test
   public void renameEmailWithSpecifiedCommitMessage() throws Exception {
-    // renaming email is not supported for the proto backend
-    assume().that(backendConfig.getDefaultBackend()).isNotInstanceOf(ProtoBackend.class);
+    skipTestIfRenameEmailNotSupportedByCodeOwnersBackend();
 
     codeOwnerConfigOperations
         .newCodeOwnerConfig()
@@ -489,8 +476,7 @@
 
   @Test
   public void renameEmail_specifiedCommitMessageIsTrimmed() throws Exception {
-    // renaming email is not supported for the proto backend
-    assume().that(backendConfig.getDefaultBackend()).isNotInstanceOf(ProtoBackend.class);
+    skipTestIfRenameEmailNotSupportedByCodeOwnersBackend();
 
     codeOwnerConfigOperations
         .newCodeOwnerConfig()
@@ -516,8 +502,7 @@
 
   @Test
   public void renameEmail_lineCommentsArePreserved() throws Exception {
-    // renaming email is not supported for the proto backend
-    assume().that(backendConfig.getDefaultBackend()).isNotInstanceOf(ProtoBackend.class);
+    skipTestIfRenameEmailNotSupportedByCodeOwnersBackend();
 
     CodeOwnerConfig.Key codeOwnerConfigKey =
         codeOwnerConfigOperations
@@ -580,8 +565,7 @@
 
   @Test
   public void renameEmail_inlineCommentsArePreserved() throws Exception {
-    // renaming email is not supported for the proto backend
-    assume().that(backendConfig.getDefaultBackend()).isNotInstanceOf(ProtoBackend.class);
+    skipTestIfRenameEmailNotSupportedByCodeOwnersBackend();
 
     CodeOwnerConfig.Key codeOwnerConfigKey =
         codeOwnerConfigOperations
@@ -642,8 +626,7 @@
 
   @Test
   public void renameEmail_emailInCommentIsReplaced() throws Exception {
-    // renaming email is not supported for the proto backend
-    assume().that(backendConfig.getDefaultBackend()).isNotInstanceOf(ProtoBackend.class);
+    skipTestIfRenameEmailNotSupportedByCodeOwnersBackend();
 
     CodeOwnerConfig.Key codeOwnerConfigKey =
         codeOwnerConfigOperations
@@ -687,8 +670,7 @@
   @Test
   public void renameEmail_emailThatContainsEmailToBeReplacesAsSubstringStaysIntact()
       throws Exception {
-    // renaming email is not supported for the proto backend
-    assume().that(backendConfig.getDefaultBackend()).isNotInstanceOf(ProtoBackend.class);
+    skipTestIfRenameEmailNotSupportedByCodeOwnersBackend();
 
     TestAccount otherUser1 =
         accountCreator.create(
@@ -745,4 +727,9 @@
         .branch(branchName)
         .renameEmailInCodeOwnerConfigFiles(input);
   }
+
+  private void skipTestIfRenameEmailNotSupportedByCodeOwnersBackend() {
+    // the proto backend doesn't support renaming emails
+    assumeThatCodeOwnersBackendIsNotProtoBackend();
+  }
 }
diff --git a/javatests/com/google/gerrit/plugins/codeowners/backend/CodeOwnersExceptionHookTest.java b/javatests/com/google/gerrit/plugins/codeowners/backend/CodeOwnersExceptionHookTest.java
index e05f8cd..c727080 100644
--- a/javatests/com/google/gerrit/plugins/codeowners/backend/CodeOwnersExceptionHookTest.java
+++ b/javatests/com/google/gerrit/plugins/codeowners/backend/CodeOwnersExceptionHookTest.java
@@ -21,6 +21,7 @@
 import com.google.gerrit.plugins.codeowners.acceptance.AbstractCodeOwnersTest;
 import com.google.gerrit.plugins.codeowners.backend.config.InvalidPluginConfigurationException;
 import com.google.gerrit.server.ExceptionHook.Status;
+import java.nio.file.InvalidPathException;
 import java.util.Optional;
 import org.eclipse.jgit.errors.ConfigInvalidException;
 import org.junit.Before;
@@ -44,6 +45,9 @@
     assertThat(skipRetryWithTrace(newConfigInvalidException())).isTrue();
     assertThat(skipRetryWithTrace(newExceptionWithCause(newConfigInvalidException()))).isTrue();
 
+    assertThat(skipRetryWithTrace(newInvalidPathException())).isTrue();
+    assertThat(skipRetryWithTrace(newExceptionWithCause(newInvalidPathException()))).isTrue();
+
     assertThat(skipRetryWithTrace(new Exception())).isFalse();
     assertThat(skipRetryWithTrace(newExceptionWithCause(new Exception()))).isFalse();
   }
@@ -63,6 +67,12 @@
     assertThat(getUserMessages(newExceptionWithCause(configInvalidException)))
         .containsExactly(configInvalidException.getMessage());
 
+    InvalidPathException invalidPathException = newInvalidPathException();
+    assertThat(getUserMessages(invalidPathException))
+        .containsExactly(invalidPathException.getMessage());
+    assertThat(getUserMessages(newExceptionWithCause(invalidPathException)))
+        .containsExactly(invalidPathException.getMessage());
+
     assertThat(getUserMessages(new Exception())).isEmpty();
     assertThat(getUserMessages(newExceptionWithCause(new Exception()))).isEmpty();
   }
@@ -82,6 +92,11 @@
         .value()
         .isEqualTo(conflictStatus);
 
+    assertThat(getStatus(newInvalidPathException())).value().isEqualTo(conflictStatus);
+    assertThat(getStatus(newExceptionWithCause(newInvalidPathException())))
+        .value()
+        .isEqualTo(conflictStatus);
+
     assertThat(getStatus(new Exception())).isEmpty();
     assertThat(getStatus(newExceptionWithCause(new Exception()))).isEmpty();
   }
@@ -109,4 +124,8 @@
   private ConfigInvalidException newConfigInvalidException() {
     return new ConfigInvalidException("message");
   }
+
+  private InvalidPathException newInvalidPathException() {
+    return new InvalidPathException("input", "reason");
+  }
 }
diff --git a/resources/Documentation/backend-find-owners.md b/resources/Documentation/backend-find-owners.md
index aa7a8b7..a1af71d 100644
--- a/resources/Documentation/backend-find-owners.md
+++ b/resources/Documentation/backend-find-owners.md
@@ -14,7 +14,7 @@
 contains an `OWNERS` file that disables the inheritance of code owners from the
 parent directories via the [set noparent](#setNoparent) keyword).
 
-<a id="defaultCodeOwnerConfiguration">
+### <a id="defaultCodeOwnerConfiguration">
 Default code owners that apply to all branches can be defined in an `OWNERS`
 file in the root directory of the `refs/meta/config` branch. This `OWNERS` file
 is the parent of the root `OWNERS` files in all branches. This means if a root
@@ -245,7 +245,7 @@
   john.doe@example.com
   per-file docs.config,*.md=richard.roe@example.com
 ```
-\
+
 ##### <a id="doNotUsePathExpressionsForSubdirectories">
 **NOTE:** It is discouraged to use path expressions that explicitly name
 subdirectories such as `my-subdir/*` as they will break when the subdirectory
diff --git a/resources/Documentation/build.md b/resources/Documentation/build.md
index a1469f4..6c2db04 100644
--- a/resources/Documentation/build.md
+++ b/resources/Documentation/build.md
@@ -10,13 +10,13 @@
 ```
   bazel build plugins/@PLUGIN@
 ```
-
+\
 The output is created in
 
 ```
   bazel-bin/plugins/@PLUGIN@/@PLUGIN@.jar
 ```
-
+\
 To execute the tests run:
 
 ```
diff --git a/resources/Documentation/path-expressions.md b/resources/Documentation/path-expressions.md
index bedbbfe..322d757 100644
--- a/resources/Documentation/path-expressions.md
+++ b/resources/Documentation/path-expressions.md
@@ -37,9 +37,9 @@
 | To Match | Glob | Simple Path Expression |
 | -------- | ---- | ---------------------- |
 | Concrete file in current folder | `BUILD` | `BUILD` |
-| File type in current folder | `*.md` | `*.md` |
+| File type in current folder | not possible | `*.md` |
 | Concrete file in the current folder and in all subfolders | `{**/,}BUILD` | needs 2 expressions: `BUILD` + `.../BUILD` |
-| File type in the current folder and in all subfolder | `**.md` | `....md` |
+| File type in the current folder and in all subfolders | `**.md` or `*.md` | `....md` |
 | All files in a subfolder | `my-folder/**` | `my-folder/...` |
 | All “foo-<1-digit-number>.txt” files in all subfolders | `{**/,}foo-[0-9].txt` | not possible |
 | All “foo-<n-digit-number>.txt” files in all subfolders | not possible | not possible |
diff --git a/resources/Documentation/setup-guide.md b/resources/Documentation/setup-guide.md
index 7449164..9a0e85f 100644
--- a/resources/Documentation/setup-guide.md
+++ b/resources/Documentation/setup-guide.md
@@ -26,6 +26,8 @@
 
 * [How to update the code-owners.config file for a project](#updateCodeOwnersConfig)
 * [How to check if the code owners functionality is enabled for a project or branch](#checkIfEnabled)
+* [How to avoid issues with code owner config files](#avoidIssuesWithCodeOwnerConfigs)
+* [How to investigate issues with code owner config files](#investigateIssuesWithCodeOwnerConfigs)
 
 Recommendations about further configuration parameters can be found in the
 [config guide](config-guide.html).
@@ -406,6 +408,53 @@
 `https://<host>/projects/<project-name>/code_owners.project_config`\
 (remember to URL-encode the project-name and branch-name)
 
+##### <a id="avoidIssuesWithCodeOwnerConfigs">How to avoid issues with code owner config files
+
+To avoid issues with code owner config files it's highly recommended to keep the
+[validation](validation.html) of code owner config files that is performed on
+receive commits and submit enabled, as it prevents that issues are newly
+introduced to code owner config files. Whether this validation is enabled and
+whether code owner config files with new issues are rejected is controlled by
+the following configuration parameters:
+
+* [plugin.@PLUGIN@.enableValidationOnCommitReceived](config.html#pluginCodeOwnersEnableValidationOnCommitReceived)
+* [plugin.@PLUGIN@.enableValidationOnSubmit](config.html#pluginCodeOwnersEnableValidationOnSubmit)
+* [plugin.@PLUGIN@.rejectNonResolvableCodeOwners](config.html#pluginCodeOwnersRejectNonResolvableCodeOwners)
+* [plugin.@PLUGIN@.rejectNonResolvableImports](config.html#pluginCodeOwnersRejectNonResolvableImports)
+
+Since code owner config files can also get
+[issues](validation.html#howCodeOwnerConfigsCanGetIssuesAfterSubmit) after they
+have been submitted, host administrators and project owners are also recommended
+to regularly check the existing code owner config files for issues by calling
+the [Check Code Owner Config File REST
+endpoint](rest-api.html#check-code-owner-config-files) (e.g. from a cronjob) and
+then fix the reported issues.
+
+##### <a id="investigateIssuesWithCodeOwnerConfigs">How to investigate issues with code owner config files
+
+If code owners config files are not working as expected, this is either caused
+by:
+
+* issues in the code owner config files
+* a bug in the @PLUGIN@ plugin
+
+Since code owner config files are part of the source code, any issues with them
+should be investigated and fixed by the project owners and host administrators.
+To do this they can:
+
+* Check the code owner config files for issues by calling the [Check Code Owner
+  Config File REST endpoint](rest-api.html#check-code-owner-config-files)
+* Check the code ownership of a user for a certain path by calling the [Check
+  Code Owner REST endpoint](rest-api.html#check-code-owner) (requires the caller
+  to be host administrator or have the [Check Code Owner
+  capability](#checkCodeOwner)).
+
+Bugs with the @PLUGIN@ plugin should be filed as issues for the Gerrit team, but
+only after issues with the code owner config files have been excluded.
+
+Also see [above](#avoidIssuesWithCodeOwnerConfigs) how to avoid issues with code
+owner config files in the first place.
+
 ---
 
 Back to [@PLUGIN@ documentation index](index.html)
diff --git a/resources/Documentation/validation.md b/resources/Documentation/validation.md
index 47c3ef5..756edd5 100644
--- a/resources/Documentation/validation.md
+++ b/resources/Documentation/validation.md
@@ -53,6 +53,7 @@
   blocking all uploads, to reduce the risk of breaking the plugin configuration
   `code-owner.config` files are validated too)
 
+## <a id="howCodeOwnerConfigsCanGetIssuesAfterSubmit">
 In addition it is possible that [code owner config
 files](user-guide.hmtl#codeOwnerConfigFiles) get issues after they have been
 submitted: