Merge pull request #767 from MateuszJajeGP/master

Fix NPE in GitLabPushTrigger

src/main/java/com/dabsquared/gitlabjenkins/GitLabPushTrigger.java

@@ -454,6 +454,9 @@ public class GitLabPushTrigger extends Trigger<Job<?, ?>> {
 
     // executes when the Trigger receives a pipeline event
     public void onPost(final PipelineHook hook) {
+        if (pipelineTriggerHandler == null) {
+            initializeTriggerHandler();
+        }
         pipelineTriggerHandler.handle(job, hook, ciSkip, branchFilter, mergeRequestLabelFilter);
     }