fix: fix nullpointerexception when body is null (#390)

* fix: fix nullpointerexception when body is null

An exception will occur when the body is null (empty) and a pr description check is configured. This change will fall back to an empty string when the body is null (and thus empty).

* chore: add test case

* fix: fixed newly added test case

Author: kvanzuijlen

github-pullrequest-plugin/src/main/java/org/jenkinsci/plugins/github/pullrequest/events/impl/GitHubPRDescriptionEvent.java

@@ -55,7 +55,7 @@ public GitHubPRCause check(@NonNull GitHubPRDecisionContext prDecisionContext) t
 
         GitHubPRCause cause = null;
 
-        String pullRequestBody = remotePR.getBody().trim();
+        String pullRequestBody = remotePR.getBody() != null ? remotePR.getBody().trim() : "";
         LOG.debug("Job: '{}', trigger event: '{}', body for test: '{}'",
                 fullName,
                 DISPLAY_NAME,

github-pullrequest-plugin/src/test/java/org/jenkinsci/plugins/github/pullrequest/events/impl/GitHubPRDescriptionEventTest.java

@@ -74,7 +74,7 @@ public void skipDescriptionExist() throws IOException {
     }
 
     @Test
-    public void skipDescriptionNotExist() throws IOException {
+    public void skipDescriptionExistNotMatch() throws IOException {
         commonExpectations();
         causeCreationExpectations();
 
@@ -93,6 +93,26 @@ public void skipDescriptionNotExist() throws IOException {
         assertThat(cause, nullValue());
     }
 
+    @Test
+    public void skipDescriptionNotExist() throws IOException {
+        commonExpectations();
+        causeCreationExpectations();
+
+        when(listener.getLogger()).thenReturn(logger);
+
+        when(remotePr.getBody()).thenReturn(null);
+
+        GitHubPRCause cause = new GitHubPRDescriptionEvent(".*[skip ci].*")
+                .check(newGitHubPRDecisionContext()
+                        .withPrTrigger(trigger)
+                        .withRemotePR(remotePr)
+                        .withListener(listener)
+                        .build()
+                );
+
+        assertThat(cause, nullValue());
+    }
+
     private void commonExpectations() throws IOException {
         when(parent.getFullName()).thenReturn("Full job name");