[JENKINS-63572] Avoid NPE if remote config is empty

src/main/java/hudson/plugins/git/GitSCM.java

@@ -851,11 +851,13 @@ public GitClient createClient(TaskListener listener, EnvVars environment, Run<?,
                 String url = getParameterString(uc.getUrl(), environment);
                 chooser = new GitToolChooser(url, project, ucCredentialsId, gitTool, n, listener,unsupportedCommand.determineSupportForJGit());
             }
-            listener.getLogger().println("The recommended git tool is: " + chooser.getGitTool());
-            String updatedGitExe = chooser.getGitTool();
-
-            if (!updatedGitExe.equals("NONE")) {
-                gitExe = updatedGitExe;
+            if (chooser != null) {
+                listener.getLogger().println("The recommended git tool is: " + chooser.getGitTool());
+                String updatedGitExe = chooser.getGitTool();
+
+                if (!updatedGitExe.equals("NONE")) {
+                    gitExe = updatedGitExe;
+                }
             }
         }
         Git git = Git.with(listener, environment).in(ws).using(gitExe);

src/test/java/jenkins/plugins/git/GitToolChooserTest.java

@@ -545,6 +545,24 @@ public void getCacheDirCreatesNoDirectory() throws Exception {
         assertThat(expectedCacheDir, is(anExistingDirectory()));
     }
 
+    /* Do not throw null pointer excception if remote configuration is empty. */
+    @Test
+    @Issue("JENKINS-63572")
+    public void testSizeEstimationWithNoRemoteConfig() throws Exception {
+        sampleRepo.init();
+
+        failAProject(sampleRepo);
+
+        List<TopLevelItem> list = jenkins.jenkins.getItems();
+
+        // Use JGit as the git tool for this NPE check
+        GitTool jgitTool = new JGitTool(Collections.<ToolProperty<?>>emptyList());
+
+        GitToolChooser sizeEstimator = new GitToolChooser(sampleRepo.toString(), list.get(0), null, jgitTool, null, TaskListener.NULL, true);
+
+        assertThat(sizeEstimator.getGitTool(), is("NONE"));
+    }
+
     /*
     A test extension implemented to clone the behavior of a plugin extending the capability of providing the size of
     repo from a remote URL of "Github".
@@ -637,6 +655,18 @@ private void buildAProject(GitSampleRepoRule sampleRepo, boolean noCredentials)
         }
     }
 
+    /* Attempt to perform a checkout without defining a remote repository. Expected to fail, but should not report NPE */
+    private void failAProject(GitSampleRepoRule sampleRepo) throws Exception {
+        WorkflowJob p = jenkins.jenkins.createProject(WorkflowJob.class, "intentionally-failing-job-without-remote-config");
+        p.setDefinition(new CpsFlowDefinition("node {\n"
+                                              + "  checkout(\n"
+                                              + "    [$class: 'GitSCM']\n"
+                                              + "  )\n"
+                                              + "}", true));
+        WorkflowRun b = jenkins.assertBuildStatus(hudson.model.Result.FAILURE, p.scheduleBuild2(0));
+        jenkins.waitForMessage("Couldn't find any revision to build", b);
+    }
+
     private StandardCredentials createCredential(CredentialsScope scope, String id) {
         return new UsernamePasswordCredentialsImpl(scope, id, "desc: " + id, "username", "password");
     }