Set "ref" in PR build status for Bitbucket Server

Author: KalleOlaviNiemitalo

src/main/java/com/cloudbees/jenkins/plugins/bitbucket/BitbucketBuildStatusNotifications.java

@@ -220,9 +220,20 @@ private static void sendNotifications(BitbucketSCMSource source, Run<?, ?> build
              * causes the build status disappear from the web page.
              * The only working value is null. If commit is used for two different
              * pull requests than you will get status doubled in both PRs
+             *
+             * For Bitbucket Server, refName should be "refs/heads/" + the name
+             * of the source branch of the pull request, and the build status
+             * should be posted to the repository that contains that branch.
+             * If refName is null, then Bitbucket Server does not show the
+             * build status in the list of pull requests, but still shows it
+             * on the web page of the individual pull request.
              */
-            refName = null; // "refs/pull-requests/" + head.getBranchName();
             bitbucket = source.buildBitbucketClient(head);
+            if (BitbucketApiUtils.isCloud(bitbucket)) {
+                refName = null; // "refs/pull-requests/" + head.getBranchName();
+            } else {
+                refName = "refs/heads/" + head.getBranchName();
+            }
         } else {
             listener.getLogger().println("[Bitbucket] Notifying commit build result");
             SCMHead head = rev.getHead();