diff --git a/src/main/java/com/googlesource/gerrit/plugins/findowners/Action.java b/src/main/java/com/googlesource/gerrit/plugins/findowners/Action.java
index 1971491..361cecc 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/findowners/Action.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/findowners/Action.java
@@ -14,13 +14,15 @@
 
 package com.googlesource.gerrit.plugins.findowners;
 
+import static java.util.stream.Collectors.toList;
+
 import com.google.common.annotations.VisibleForTesting;
+import com.google.common.collect.Streams;
 import com.google.gerrit.extensions.annotations.PluginName;
 import com.google.gerrit.extensions.restapi.BadRequestException;
 import com.google.gerrit.extensions.restapi.Response;
 import com.google.gerrit.extensions.restapi.RestReadView;
 import com.google.gerrit.extensions.webui.UiAction;
-import com.google.gerrit.reviewdb.client.Account;
 import com.google.gerrit.reviewdb.client.Change;
 import com.google.gerrit.reviewdb.client.Change.Status;
 import com.google.gerrit.reviewdb.server.ReviewDb;
@@ -46,6 +48,7 @@
 import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
+import java.util.Objects;
 import java.util.Set;
 import org.eclipse.jgit.lib.Repository;
 import org.slf4j.Logger;
@@ -141,17 +144,21 @@
 
   /** Returns reviewer emails got from ChangeData. */
   static List<String> getReviewers(ChangeData changeData, AccountCache accountCache) {
-    List<String> result = new ArrayList<>();
     try {
-      for (Account.Id id : changeData.reviewers().all()) {
-        Account account = accountCache.get(id).getAccount();
-        result.add(account.getPreferredEmail());
-      }
+      // Reviewers may have no preferred email, skip them if the preferred email is not set.
+      return changeData
+          .reviewers()
+          .all()
+          .stream()
+          .map(accountCache::get)
+          .flatMap(Streams::stream)
+          .map(a -> a.getAccount().getPreferredEmail())
+          .filter(Objects::nonNull)
+          .collect(toList());
     } catch (OrmException e) {
       log.error("Exception for " + Config.getChangeId(changeData), e);
-      result = new ArrayList<>();
+      return new ArrayList<>();
     }
-    return result;
   }
 
   /** Returns the current patchset number or the given patchsetNum if it is valid. */
diff --git a/src/main/java/com/googlesource/gerrit/plugins/findowners/Checker.java b/src/main/java/com/googlesource/gerrit/plugins/findowners/Checker.java
index 85f4bec..54861a1 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/findowners/Checker.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/findowners/Checker.java
@@ -26,6 +26,7 @@
 import java.io.IOException;
 import java.util.HashMap;
 import java.util.Map;
+import java.util.Optional;
 import java.util.Set;
 import org.eclipse.jgit.lib.Repository;
 import org.slf4j.Logger;
@@ -55,16 +56,24 @@
     Map<String, Integer> map = new HashMap<>();
     for (PatchSetApproval p : changeData.currentApprovals()) {
       if (p.getValue() != 0) {
-        map.put(
-            accountCache.get(p.getAccountId()).getAccount().getPreferredEmail(),
-            Integer.valueOf(p.getValue()));
+        // Reviewers may have no preferred email, skip them if the preferred email is not set.
+        Optional<String> preferredEmail =
+            accountCache.get(p.getAccountId()).map(a -> a.getAccount().getPreferredEmail());
+        if (preferredEmail.isPresent()) {
+          map.put(preferredEmail.get(), Integer.valueOf(p.getValue()));
+        }
       }
     }
     // Give CL author a default minVoteLevel vote.
-    String author =
-        accountCache.get(changeData.change().getOwner()).getAccount().getPreferredEmail();
-    if (!map.containsKey(author) || map.get(author) == 0) {
-      map.put(author, minVoteLevel);
+    // The preferred email of the author may not be set. Pushing changes only requires an email in
+    // the external IDs, but the preferred email may still be null (also emails may have been
+    // deleted after creating the change). Skip the author if it doesn't have a preferred email.
+    Optional<String> author =
+        accountCache
+            .get(changeData.change().getOwner())
+            .map(a -> a.getAccount().getPreferredEmail());
+    if (author.isPresent() && (!map.containsKey(author.get()) || map.get(author.get()) == 0)) {
+      map.put(author.get(), minVoteLevel);
     }
     return map;
   }
diff --git a/src/main/java/com/googlesource/gerrit/plugins/findowners/OwnersDb.java b/src/main/java/com/googlesource/gerrit/plugins/findowners/OwnersDb.java
index 2c0c704..bd84c13 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/findowners/OwnersDb.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/findowners/OwnersDb.java
@@ -152,7 +152,12 @@
             if (ids == null || ids.size() != 1) {
               errors.add(owner);
             } else {
-              email = accountCache.get(ids.iterator().next()).getAccount().getPreferredEmail();
+              // Accounts may have no preferred email.
+              email =
+                  accountCache
+                      .get(ids.iterator().next())
+                      .map(a -> a.getAccount().getPreferredEmail())
+                      .orElse(null);
             }
           }
         } catch (Exception e) {
diff --git a/src/test/java/com/googlesource/gerrit/plugins/findowners/FindOwnersIT.java b/src/test/java/com/googlesource/gerrit/plugins/findowners/FindOwnersIT.java
index 9ad5140..323a861 100644
--- a/src/test/java/com/googlesource/gerrit/plugins/findowners/FindOwnersIT.java
+++ b/src/test/java/com/googlesource/gerrit/plugins/findowners/FindOwnersIT.java
@@ -15,6 +15,7 @@
 package com.googlesource.gerrit.plugins.findowners;
 
 import static com.google.common.truth.Truth.assertThat;
+import static com.google.common.truth.Truth8.assertThat;
 import static com.google.gerrit.reviewdb.client.RefNames.REFS_CONFIG;
 import static java.nio.charset.StandardCharsets.UTF_8;
 
@@ -32,11 +33,13 @@
 import com.google.gerrit.reviewdb.client.Account;
 import com.google.gerrit.reviewdb.client.Project;
 import com.google.gerrit.reviewdb.client.RefNames;
+import com.google.gerrit.server.account.AccountState;
 import com.google.gerrit.server.account.Emails;
 import com.google.gerrit.server.change.ChangeResource;
 import com.google.gerrit.server.config.PluginConfigFactory;
 import com.google.inject.Inject;
 import java.util.Collection;
+import java.util.Optional;
 import org.eclipse.jgit.lib.ObjectLoader;
 import org.eclipse.jgit.lib.Repository;
 import org.eclipse.jgit.revwalk.RevObject;
@@ -208,7 +211,9 @@
       assertThat(id1).isEqualTo(id3);
       assertThat(id1).isEqualTo(id4);
       // Action.getReviewers and Checker.getVotes use accountCache to get email address.
-      assertThat(accountCache.get(id1).getAccount().getPreferredEmail()).isEqualTo(emails1[i]);
+      Optional<Account> account = accountCache.get(id1).map(AccountState::getAccount);
+      assertThat(account).named("account %s", id1).isPresent();
+      assertThat(account.get().getPreferredEmail()).isEqualTo(emails1[i]);
     }
     // Wrong or non-existing email address.
     String[] wrongEmails = {"nobody", "@g.com", "nobody@g.com", "*"};