apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/component/emailbuilder/ConfigPublishEmailBuilder.java/ConfigPublishEmailBuilder/getReleaseCompareResult
class ConfigPublishEmailBuilder:  private ReleaseCompareResult getReleaseCompareResult(Env env, ReleaseHistoryBO releaseHistory) {
    if (releaseHistory.getOperation() == ReleaseOperation.GRAY_RELEASE
            && releaseHistory.getPreviousReleaseId() == 0) {
      ReleaseDTO masterLatestActiveRelease = releaseService.loadLatestRelease(
              releaseHistory.getAppId(), env, releaseHistory.getClusterName(), releaseHistory.getNamespaceName());
      ReleaseDTO branchLatestActiveRelease = releaseService.findReleaseById(env, releaseHistory.getReleaseId());

      return releaseService.compare(masterLatestActiveRelease, branchLatestActiveRelease);
    }

    return releaseService.compare(env, releaseHistory.getPreviousReleaseId(), releaseHistory.getReleaseId());
  }