Fix NPE in ReverseBuildTrigger due to null upstream threshold (#23916)

* Fix NPE in ReverseBuildTrigger due to null upstream threshold (JENKINS-39044)

* Use ReverseTrigger constructor that is not deprecated

Has the same result as the deprecated constructor that was used before.

* Add automated test of JENKINS-39044

If the ReverseTrigger threshold were null, a null pointer exception would
be thrown.  The config round trip operation resets a null threshold to
SUCCESS, so this test reaches inside the job definition and changes the
threshold directly.

Testing done:

* Confirmed that the modified automated test fails when the change to
  ReverseTrigger is removed.
* Confirmed that the modified automated test passes when the change to
  ReverseTrigger is included.

* Link to GitHub issue

---------

Co-authored-by: Mark Waite <[email protected]>

Author: Zenith1415

core/src/main/java/jenkins/triggers/ReverseBuildTrigger.java

@@ -166,7 +166,7 @@ private boolean shouldTrigger(Run upstreamBuild, TaskListener listener) {
             return false;
         }
         Result result = upstreamBuild.getResult();
-        return result != null && result.isBetterOrEqualTo(threshold);
+        return result != null && result.isBetterOrEqualTo(threshold != null ? threshold : Result.SUCCESS);
     }
 
     @Override public void buildDependencyGraph(final AbstractProject downstream, DependencyGraph graph) {

test/src/test/java/jenkins/triggers/ReverseBuildTriggerTest.java

@@ -189,25 +189,30 @@ void upstreamProjectSecurity() throws Exception {
         assertEquals(3, downstream.getLastBuild().number);
     }
 
-    @Issue("JENKINS-29876")
+    @Issue({"JENKINS-29876", "JENKINS-39044", "https://github.com/jenkinsci/jenkins/issues/17611"})
     @Test
     void nullJobInTriggerNotCausesNPE() throws Exception {
         final FreeStyleProject upstreamJob = r.createFreeStyleProject("upstream");
 
         //job with trigger.job == null
         final FreeStyleProject downstreamJob1 = r.createFreeStyleProject("downstream1");
-        final ReverseBuildTrigger reverseBuildTrigger = new ReverseBuildTrigger("upstream", Result.SUCCESS);
+        final ReverseBuildTrigger reverseBuildTrigger = new ReverseBuildTrigger("upstream");
         downstreamJob1.addTrigger(reverseBuildTrigger);
         downstreamJob1.save();
 
         //job with trigger.job != null
         final FreeStyleProject downstreamJob2 = r.createFreeStyleProject("downstream2");
-        final ReverseBuildTrigger reverseBuildTrigger2 = new ReverseBuildTrigger("upstream", Result.SUCCESS);
+        final ReverseBuildTrigger reverseBuildTrigger2 = new ReverseBuildTrigger("upstream");
         downstreamJob2.addTrigger(reverseBuildTrigger2);
         downstreamJob2.save();
         r.configRoundtrip(downstreamJob2);
 
         r.jenkins.rebuildDependencyGraph();
+
+        // JENKINS-39044 - NPE if trigger threshold is null
+        ReverseBuildTrigger trigger = downstreamJob2.getTrigger(ReverseBuildTrigger.class);
+        trigger.setThreshold(null);
+
         final FreeStyleBuild build = r.buildAndAssertSuccess(upstreamJob);
         r.waitUntilNoActivity();