compareCommits return empty

[XSDYS]

public GitlabCommitComparison compareCommits(Serializable projectId, String commitHash1, String commitHash2) throws IOException {
    return this.compareCommits(projectId, commitHash1, commitHash2, new Pagination());
}

Hello, I use this method to compare the diff of two commits, but I found that if the git page displays "This diff is collapsed. Click to expand it" the return will also be empty.

{
  "aMode": "0",
  "bMode": "100644",
  "deletedFile": false,
  "diff": "",
  "newFile": true,
  "newPath": "src/main/java/com/qunhe/instdeco/diy/rps/logic/videorender/VideoObjectEditLogic.java",
  "oldPath": "src/main/java/com/qunhe/instdeco/diy/rps/logic/videorender/VideoObjectEditLogic.java",
  "renamedFile": false
}