diff --git a/java/com/google/gerrit/server/patch/DiffOperationsImpl.java b/java/com/google/gerrit/server/patch/DiffOperationsImpl.java
index fd30868..01a577a 100644
--- a/java/com/google/gerrit/server/patch/DiffOperationsImpl.java
+++ b/java/com/google/gerrit/server/patch/DiffOperationsImpl.java
@@ -16,7 +16,6 @@
 
 import static com.google.gerrit.entities.Patch.COMMIT_MSG;
 import static com.google.gerrit.entities.Patch.MERGE_LIST;
-import static org.eclipse.jgit.lib.Constants.EMPTY_TREE_ID;
 
 import com.google.auto.value.AutoValue;
 import com.google.common.collect.ImmutableList;
@@ -346,7 +345,7 @@
 
     /**
      * Base commit represents the old commit of the diff. For diffs against the root commit, this
-     * should be set to {@code EMPTY_TREE_ID}.
+     * should be set to {@link ObjectId#zeroId()}.
      */
     abstract ObjectId baseCommit();
 
@@ -394,7 +393,7 @@
     }
     int numParents = baseCommitUtil.getNumParents(project, newCommit);
     if (numParents == 0) {
-      result.baseCommit(EMPTY_TREE_ID);
+      result.baseCommit(ObjectId.zeroId());
       result.comparisonType(ComparisonType.againstRoot());
       return result.build();
     }
diff --git a/java/com/google/gerrit/server/patch/diff/ModifiedFilesCache.java b/java/com/google/gerrit/server/patch/diff/ModifiedFilesCache.java
index bcae238..56f49c9 100644
--- a/java/com/google/gerrit/server/patch/diff/ModifiedFilesCache.java
+++ b/java/com/google/gerrit/server/patch/diff/ModifiedFilesCache.java
@@ -28,8 +28,8 @@
  * files.
  *
  * <p>If the {@link ModifiedFilesCacheKey#aCommit()} is equal to {@link
- * org.eclipse.jgit.lib.Constants#EMPTY_TREE_ID}, the diff will be evaluated against the empty tree,
- * and the result will be exactly the same as the caller can get from {@link
+ * org.eclipse.jgit.lib.ObjectId#zeroId()}, the diff will be evaluated against the empty tree, and
+ * the result will be exactly the same as the caller can get from {@link
  * GitModifiedFilesCache#get(GitModifiedFilesCacheKey)}
  */
 public interface ModifiedFilesCache {
diff --git a/java/com/google/gerrit/server/patch/diff/ModifiedFilesCacheImpl.java b/java/com/google/gerrit/server/patch/diff/ModifiedFilesCacheImpl.java
index e168386..b779bf7 100644
--- a/java/com/google/gerrit/server/patch/diff/ModifiedFilesCacheImpl.java
+++ b/java/com/google/gerrit/server/patch/diff/ModifiedFilesCacheImpl.java
@@ -15,7 +15,6 @@
 package com.google.gerrit.server.patch.diff;
 
 import static com.google.common.collect.ImmutableList.toImmutableList;
-import static org.eclipse.jgit.lib.Constants.EMPTY_TREE_ID;
 
 import com.google.common.cache.CacheLoader;
 import com.google.common.cache.LoadingCache;
@@ -52,10 +51,9 @@
  * <p>The loader of this cache wraps a {@link GitModifiedFilesCache} to retrieve the git modified
  * files.
  *
- * <p>If the {@link ModifiedFilesCacheKey#aCommit()} is equal to {@link
- * org.eclipse.jgit.lib.Constants#EMPTY_TREE_ID}, the diff will be evaluated against the empty tree,
- * and the result will be exactly the same as the caller can get from {@link
- * GitModifiedFilesCache#get(GitModifiedFilesCacheKey)}
+ * <p>If the {@link ModifiedFilesCacheKey#aCommit()} is equal to {@link ObjectId#zeroId()}, the diff
+ * will be evaluated against the empty tree, and the result will be exactly the same as the caller
+ * can get from {@link GitModifiedFilesCache#get(GitModifiedFilesCacheKey)}
  */
 @Singleton
 public class ModifiedFilesCacheImpl implements ModifiedFilesCache {
@@ -130,7 +128,7 @@
     private ImmutableList<ModifiedFile> loadModifiedFiles(ModifiedFilesCacheKey key, RevWalk rw)
         throws IOException, DiffNotAvailableException {
       ObjectId aTree =
-          key.aCommit().equals(EMPTY_TREE_ID)
+          key.aCommit().equals(ObjectId.zeroId())
               ? key.aCommit()
               : DiffUtil.getTreeId(rw, key.aCommit());
       ObjectId bTree = DiffUtil.getTreeId(rw, key.bCommit());
@@ -142,7 +140,7 @@
               .renameScore(key.renameScore())
               .build();
       List<ModifiedFile> modifiedFiles = gitCache.get(gitKey);
-      if (key.aCommit().equals(EMPTY_TREE_ID)) {
+      if (key.aCommit().equals(ObjectId.zeroId())) {
         return ImmutableList.copyOf(modifiedFiles);
       }
       RevCommit revCommitA = DiffUtil.getRevCommit(rw, key.aCommit());
diff --git a/java/com/google/gerrit/server/patch/filediff/AllDiffsEvaluator.java b/java/com/google/gerrit/server/patch/filediff/AllDiffsEvaluator.java
index 12decc3..9afa1e0 100644
--- a/java/com/google/gerrit/server/patch/filediff/AllDiffsEvaluator.java
+++ b/java/com/google/gerrit/server/patch/filediff/AllDiffsEvaluator.java
@@ -14,8 +14,6 @@
 
 package com.google.gerrit.server.patch.filediff;
 
-import static org.eclipse.jgit.lib.Constants.EMPTY_TREE_ID;
-
 import com.google.common.collect.ImmutableMap;
 import com.google.common.flogger.FluentLogger;
 import com.google.gerrit.server.patch.DiffNotAvailableException;
@@ -203,7 +201,7 @@
       FileDiffCacheKey key, ObjectId aCommit, ObjectId bCommit, String pathNew, RevWalk rw)
       throws IOException {
     ObjectId oldTreeId =
-        aCommit.equals(EMPTY_TREE_ID) ? EMPTY_TREE_ID : DiffUtil.getTreeId(rw, aCommit);
+        aCommit.equals(ObjectId.zeroId()) ? ObjectId.zeroId() : DiffUtil.getTreeId(rw, aCommit);
     ObjectId newTreeId = DiffUtil.getTreeId(rw, bCommit);
     return GitFileDiffCacheKey.builder()
         .project(key.project())
diff --git a/java/com/google/gerrit/server/patch/filediff/FileDiffCacheImpl.java b/java/com/google/gerrit/server/patch/filediff/FileDiffCacheImpl.java
index ee5e156..c05aae0 100644
--- a/java/com/google/gerrit/server/patch/filediff/FileDiffCacheImpl.java
+++ b/java/com/google/gerrit/server/patch/filediff/FileDiffCacheImpl.java
@@ -16,7 +16,6 @@
 
 import static com.google.common.collect.ImmutableList.toImmutableList;
 import static java.nio.charset.StandardCharsets.UTF_8;
-import static org.eclipse.jgit.lib.Constants.EMPTY_TREE_ID;
 
 import com.google.common.cache.CacheLoader;
 import com.google.common.cache.LoadingCache;
@@ -76,9 +75,8 @@
  * Cache for the single file diff between two commits for a single file path. This cache adds extra
  * Gerrit logic such as identifying edits due to rebase.
  *
- * <p>If the {@link FileDiffCacheKey#oldCommit()} is equal to {@link
- * org.eclipse.jgit.lib.Constants#EMPTY_TREE_ID}, the git diff will be evaluated against the empty
- * tree.
+ * <p>If the {@link FileDiffCacheKey#oldCommit()} is equal to {@link ObjectId#zeroId()}, the git
+ * diff will be evaluated against the empty tree.
  */
 @Singleton
 public class FileDiffCacheImpl implements FileDiffCache {
@@ -204,7 +202,7 @@
     private ComparisonType getComparisonType(
         RevWalk rw, ObjectReader reader, ObjectId oldCommitId, ObjectId newCommitId)
         throws IOException {
-      if (oldCommitId.equals(EMPTY_TREE_ID)) {
+      if (oldCommitId.equals(ObjectId.zeroId())) {
         return ComparisonType.againstRoot();
       }
       RevCommit oldCommit = DiffUtil.getRevCommit(rw, oldCommitId);
@@ -238,7 +236,7 @@
         ComparisonType comparisonType =
             getComparisonType(rw, reader, key.oldCommit(), key.newCommit());
         RevCommit aCommit =
-            key.oldCommit().equals(EMPTY_TREE_ID)
+            key.oldCommit().equals(ObjectId.zeroId())
                 ? null
                 : DiffUtil.getRevCommit(rw, key.oldCommit());
         RevCommit bCommit = DiffUtil.getRevCommit(rw, key.newCommit());
@@ -345,7 +343,7 @@
       FileHeader fileHeader = new FileHeader(rawHdr, edits, PatchType.UNIFIED);
       Patch.ChangeType changeType = FileHeaderUtil.getChangeType(fileHeader);
       return FileDiffOutput.builder()
-          .oldCommitId(oldCommit == null ? EMPTY_TREE_ID : oldCommit)
+          .oldCommitId(oldCommit == null ? ObjectId.zeroId() : oldCommit)
           .newCommitId(newCommit)
           .comparisonType(comparisonType)
           .oldPath(FileHeaderUtil.getOldPath(fileHeader))
@@ -399,12 +397,14 @@
         }
         List<Edit> rebaseEdits = rebaseFileEdits.edits();
 
-        RevTree aTree = rw.parseTree(allDiffs.mainDiff().gitKey().oldTree());
+        ObjectId oldTreeId = allDiffs.mainDiff().gitKey().oldTree();
+
+        RevTree aTree = oldTreeId.equals(ObjectId.zeroId()) ? null : rw.parseTree(oldTreeId);
         RevTree bTree = rw.parseTree(allDiffs.mainDiff().gitKey().newTree());
         GitFileDiff mainGitDiff = allDiffs.mainDiff().gitDiff();
 
         Long oldSize =
-            mainGitDiff.oldMode().isPresent() && mainGitDiff.oldPath().isPresent()
+            aTree != null && mainGitDiff.oldMode().isPresent() && mainGitDiff.oldPath().isPresent()
                 ? new FileSizeEvaluator(reader, aTree)
                     .compute(
                         mainGitDiff.oldId(),
@@ -453,7 +453,7 @@
     private List<AugmentedFileDiffCacheKey> wrapKeys(List<FileDiffCacheKey> keys, RevWalk rw) {
       List<AugmentedFileDiffCacheKey> result = new ArrayList<>();
       for (FileDiffCacheKey key : keys) {
-        if (key.oldCommit().equals(EMPTY_TREE_ID)) {
+        if (key.oldCommit().equals(ObjectId.zeroId())) {
           result.add(AugmentedFileDiffCacheKey.builder().key(key).ignoreRebase(true).build());
           continue;
         }
diff --git a/java/com/google/gerrit/server/patch/filediff/FileDiffCacheKey.java b/java/com/google/gerrit/server/patch/filediff/FileDiffCacheKey.java
index 7ac9343..1c0e141 100644
--- a/java/com/google/gerrit/server/patch/filediff/FileDiffCacheKey.java
+++ b/java/com/google/gerrit/server/patch/filediff/FileDiffCacheKey.java
@@ -26,7 +26,6 @@
 import com.google.gerrit.server.cache.serialize.CacheSerializer;
 import com.google.gerrit.server.cache.serialize.ObjectIdConverter;
 import com.google.gerrit.server.patch.gitfilediff.GitFileDiffCacheImpl.DiffAlgorithm;
-import org.eclipse.jgit.lib.Constants;
 import org.eclipse.jgit.lib.ObjectId;
 
 /** Cache key for the {@link FileDiffCache}. */
@@ -38,7 +37,7 @@
 
   /**
    * The 20 bytes SHA-1 commit ID of the old commit used in the diff. If set to {@link
-   * Constants#EMPTY_TREE_ID}, the diff is performed against the root commit.
+   * ObjectId#zeroId()}, an empty tree is used for the diff.
    */
   public abstract ObjectId oldCommit();
 
diff --git a/java/com/google/gerrit/server/patch/gitdiff/GitModifiedFilesCacheImpl.java b/java/com/google/gerrit/server/patch/gitdiff/GitModifiedFilesCacheImpl.java
index 9b96da1..b7144d7 100644
--- a/java/com/google/gerrit/server/patch/gitdiff/GitModifiedFilesCacheImpl.java
+++ b/java/com/google/gerrit/server/patch/gitdiff/GitModifiedFilesCacheImpl.java
@@ -39,6 +39,7 @@
 import org.eclipse.jgit.diff.DiffEntry;
 import org.eclipse.jgit.diff.DiffEntry.ChangeType;
 import org.eclipse.jgit.diff.DiffFormatter;
+import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.lib.ObjectReader;
 import org.eclipse.jgit.lib.Repository;
 import org.eclipse.jgit.util.io.DisabledOutputStream;
@@ -132,7 +133,7 @@
         }
         // The scan method only returns the file paths that are different. Callers may choose to
         // format these paths themselves.
-        return df.scan(key.aTree(), key.bTree());
+        return df.scan(key.aTree().equals(ObjectId.zeroId()) ? null : key.aTree(), key.bTree());
       }
     }
 
diff --git a/java/com/google/gerrit/server/patch/gitdiff/GitModifiedFilesCacheKey.java b/java/com/google/gerrit/server/patch/gitdiff/GitModifiedFilesCacheKey.java
index fb8fce1..16b0e65 100644
--- a/java/com/google/gerrit/server/patch/gitdiff/GitModifiedFilesCacheKey.java
+++ b/java/com/google/gerrit/server/patch/gitdiff/GitModifiedFilesCacheKey.java
@@ -37,7 +37,8 @@
 
   /**
    * The git SHA-1 {@link ObjectId} of the first git tree object for which the diff should be
-   * computed.
+   * computed. If equals to {@link ObjectId#zeroId()}, a null tree is used for the diff scan, and
+   * {@link #bTree()} is treated as an added tree.
    */
   public abstract ObjectId aTree();
 
diff --git a/java/com/google/gerrit/server/patch/gitfilediff/GitFileDiffCacheImpl.java b/java/com/google/gerrit/server/patch/gitfilediff/GitFileDiffCacheImpl.java
index 31afd17..761910f 100644
--- a/java/com/google/gerrit/server/patch/gitfilediff/GitFileDiffCacheImpl.java
+++ b/java/com/google/gerrit/server/patch/gitfilediff/GitFileDiffCacheImpl.java
@@ -219,7 +219,9 @@
         throws IOException {
       Set<String> filePathsSet = ImmutableSet.copyOf(filePaths);
       List<DiffEntry> diffEntries =
-          diffFormatter.scan(diffOptions.oldTree(), diffOptions.newTree());
+          diffFormatter.scan(
+              diffOptions.oldTree().equals(ObjectId.zeroId()) ? null : diffOptions.oldTree(),
+              diffOptions.newTree());
 
       return diffEntries.stream()
           .filter(d -> filePathsSet.contains(pathExtractor.apply(d)))
diff --git a/java/com/google/gerrit/server/patch/gitfilediff/GitFileDiffCacheKey.java b/java/com/google/gerrit/server/patch/gitfilediff/GitFileDiffCacheKey.java
index f104388..4fc5279 100644
--- a/java/com/google/gerrit/server/patch/gitfilediff/GitFileDiffCacheKey.java
+++ b/java/com/google/gerrit/server/patch/gitfilediff/GitFileDiffCacheKey.java
@@ -34,7 +34,11 @@
   /** A specific git project / repository. */
   public abstract Project.NameKey project();
 
-  /** The old 20 bytes SHA-1 git tree ID used in the git tree diff */
+  /**
+   * The old 20 bytes SHA-1 git tree ID used in the git tree diff. If equals to {@link
+   * ObjectId#zeroId()}, a null tree is used for the diff scan, and {@link #newTree()} ()} is
+   * treated as an added tree.
+   */
   public abstract ObjectId oldTree();
 
   /** The new 20 bytes SHA-1 git tree ID used in the git tree diff */
diff --git a/javatests/com/google/gerrit/acceptance/api/revision/RevisionDiffIT.java b/javatests/com/google/gerrit/acceptance/api/revision/RevisionDiffIT.java
index 1a55b82..d8dab33 100644
--- a/javatests/com/google/gerrit/acceptance/api/revision/RevisionDiffIT.java
+++ b/javatests/com/google/gerrit/acceptance/api/revision/RevisionDiffIT.java
@@ -26,7 +26,6 @@
 import static com.google.gerrit.testing.GerritJUnit.assertThrows;
 import static java.util.stream.Collectors.joining;
 import static java.util.stream.Collectors.toMap;
-import static org.eclipse.jgit.lib.Constants.EMPTY_TREE_ID;
 
 import com.google.common.base.Joiner;
 import com.google.common.collect.ImmutableList;
@@ -161,7 +160,7 @@
             modifiedFiles.values().stream()
                 .map(FileDiffOutput::oldCommitId)
                 .collect(Collectors.toSet()))
-        .containsExactly(EMPTY_TREE_ID);
+        .containsExactly(ObjectId.zeroId());
     assertThat(modifiedFiles.get("/COMMIT_MSG").changeType()).isEqualTo(Patch.ChangeType.ADDED);
     assertThat(modifiedFiles.get("f.txt").changeType()).isEqualTo(Patch.ChangeType.ADDED);
   }