private Change @Nullable [] getChanges() {
    final VcsFileRevision[] revisions = getSelectedRevisions();

    if (revisions.length > 0) {
      Arrays.sort(revisions, comparing(VcsRevisionDescription::getRevisionNumber));

      for (VcsFileRevision revision : revisions) {
        if (!myHistorySession.isContentAvailable(revision)) {
          return null;
        }
      }

      final ContentRevision startRevision = new LoadedContentRevision(myFilePath, revisions[0], myVcs.getProject());
      final ContentRevision endRevision = (revisions.length == 1) ? new CurrentContentRevision(myFilePath) :
                                          new LoadedContentRevision(myFilePath, revisions[revisions.length - 1], myVcs.getProject());

      return new Change[]{new Change(startRevision, endRevision)};
    }
    return null;
  }
private Change @Nullable [] getChanges()