scmRevisionHash might be null, prevent a NPE when calling 'ObjectId.fromString(scmRevisionHash)' (jenkinsci#1146)

Author: stmlange

src/main/java/com/dabsquared/gitlabjenkins/util/CommitStatusUpdater.java

@@ -188,6 +188,10 @@ private static List<GitLabBranchBuild> retrieveGitlabProjectIds(Run<?, ?> build,
                     return result;
                 }
                 scmRevisionHash = ((AbstractGitSCMSource.SCMRevisionImpl) scmRevision).getHash();
+                if (scmRevisionHash == null) {
+                    LOGGER.log(Level.INFO, "Build does not contain SCM revision hash.");
+                    return result;
+                }
 
                 for (final BuildData buildData : buildDatas) {
                     for (final Entry<String, Build> buildByBranchName : buildData.getBuildsByBranchName().entrySet()) {