Refactoring and simplifying the codebase

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

@@ -51,6 +51,7 @@
 import java.io.ObjectStreamException;
 import java.security.SecureRandom;
 import java.util.Collection;
+import java.util.Objects;
 import jenkins.model.Jenkins;
 import jenkins.model.ParameterizedJobMixIn;
 import jenkins.triggers.SCMTriggerItem.SCMTriggerItems;
@@ -191,10 +192,10 @@
     @Initializer(after = InitMilestone.JOB_LOADED)
     public static void migrateJobs() throws IOException {
         GitLabPushTrigger.DescriptorImpl oldConfig = Trigger.all().get(GitLabPushTrigger.DescriptorImpl.class);
-        if (!oldConfig.jobsMigrated) {
-            GitLabConnectionConfig gitLabConfig =
-                    (GitLabConnectionConfig) Jenkins.getInstance().getDescriptor(GitLabConnectionConfig.class);
-            gitLabConfig
+        if (oldConfig != null && !oldConfig.jobsMigrated) {
+            GitLabConnectionConfig gitLabConfig = (GitLabConnectionConfig)
+                    Objects.requireNonNull(Jenkins.getInstance()).getDescriptor(GitLabConnectionConfig.class);
+            Objects.requireNonNull(gitLabConfig)
                     .getConnections()
                     .add(new GitLabConnection(
                             oldConfig.gitlabHostUrl,
@@ -220,8 +221,9 @@
             oldConfig.jobsMigrated = true;
             oldConfig.save();
         }
-        if (!oldConfig.jobsMigrated2) {
-            for (AbstractProject<?, ?> project : Jenkins.getInstance().getAllItems(AbstractProject.class)) {
+        if (oldConfig != null && !oldConfig.jobsMigrated2) {
+            for (AbstractProject<?, ?> project :
+                    Objects.requireNonNull(Jenkins.getInstance()).getAllItems(AbstractProject.class)) {
                 GitLabPushTrigger trigger = project.getTrigger(GitLabPushTrigger.class);
                 if (trigger != null) {
                     if (trigger.addNoteOnMergeRequest) {
@@ -662,7 +664,7 @@
 
         private StringBuilder retrieveProjectUrl(Job<?, ?> project) {
             return new StringBuilder()
-                    .append(Jenkins.getInstance().getRootUrl())
+                    .append(Objects.requireNonNull(Jenkins.getInstance()).getRootUrl())
                     .append(GitLabWebHook.WEBHOOK_URL)
                     .append(retrieveParentUrl(project))
                     .append('/')

src/main/java/com/dabsquared/gitlabjenkins/gitlab/api/GitLabClientBuilder.java

@@ -8,6 +8,7 @@
 import java.util.ArrayList;
 import java.util.List;
 import java.util.NoSuchElementException;
+import java.util.Objects;
 import jenkins.model.Jenkins;
 import org.kohsuke.accmod.Restricted;
 import org.kohsuke.accmod.restrictions.NoExternalUse;
@@ -25,8 +26,8 @@ public static GitLabClientBuilder getGitLabClientBuilderById(String id) {
     }
 
     public static List<GitLabClientBuilder> getAllGitLabClientBuilders() {
-        List<GitLabClientBuilder> builders =
-                new ArrayList<>(Jenkins.getInstance().getExtensionList(GitLabClientBuilder.class));
+        List<GitLabClientBuilder> builders = new ArrayList<>(
+                Objects.requireNonNull(Jenkins.getInstance()).getExtensionList(GitLabClientBuilder.class));
         sort(builders);
         return builders;
     }

src/main/java/com/dabsquared/gitlabjenkins/publisher/GitLabMessagePublisher.java

@@ -13,6 +13,7 @@
 import java.text.MessageFormat;
 import java.util.HashMap;
 import java.util.Map;
+import java.util.Objects;
 import java.util.logging.Level;
 import java.util.logging.Logger;
 import javax.ws.rs.ProcessingException;
@@ -245,11 +246,11 @@ private String getNote(Run<?, ?> build, TaskListener listener) {
             message = replaceMacros(build, listener, this.getFailureNoteText());
         } else {
             String icon = getResultIcon(build.getResult());
-            String buildUrl = Jenkins.getInstance().getRootUrl() + build.getUrl();
+            String buildUrl = Objects.requireNonNull(Jenkins.getInstance()).getRootUrl() + build.getUrl();
             message = MessageFormat.format(
                     "{0} Jenkins Build {1}\n\nResults available at: [Jenkins [{2} #{3}]]({4})",
                     icon,
-                    build.getResult().toString(),
+                    Objects.requireNonNull(build.getResult()).toString(),
                     build.getParent().getDisplayName(),
                     build.getNumber(),
                     buildUrl);

src/main/java/com/dabsquared/gitlabjenkins/trigger/handler/PendingBuildsHandler.java

@@ -12,6 +12,7 @@
 import hudson.model.Cause;
 import hudson.model.Job;
 import hudson.model.Queue;
+import java.util.Objects;
 import java.util.logging.Level;
 import java.util.logging.Logger;
 import jenkins.model.Jenkins;
@@ -24,7 +25,7 @@ public class PendingBuildsHandler {
     private static final Logger LOGGER = Logger.getLogger(PendingBuildsHandler.class.getName());
 
     public void cancelPendingBuilds(Job<?, ?> job, Integer projectId, String branch) {
-        Queue queue = Jenkins.getInstance().getQueue();
+        Queue queue = Objects.requireNonNull(Jenkins.getInstance()).getQueue();
         for (Queue.Item item : queue.getItems()) {
             if (!job.getName().equals(item.task.getName())) {
                 continue;

src/main/java/com/dabsquared/gitlabjenkins/webhook/build/BuildWebHookAction.java

@@ -11,6 +11,7 @@
 import java.nio.charset.StandardCharsets;
 import java.security.MessageDigest;
 import java.security.NoSuchAlgorithmException;
+import java.util.Objects;
 import java.util.logging.Logger;
 import jenkins.model.Jenkins;
 import org.acegisecurity.Authentication;
@@ -88,7 +89,8 @@ public void run() {
         }
 
         private void checkPermission(Permission permission, Item project) {
-            if (((GitLabConnectionConfig) Jenkins.get().getDescriptor(GitLabConnectionConfig.class))
+            if (((GitLabConnectionConfig)
+                            Objects.requireNonNull(Jenkins.get().getDescriptor(GitLabConnectionConfig.class)))
                     .isUseAuthenticatedEndpoint()) {
                 if (!project.getACL().hasPermission(authentication, permission)) {
                     String message = String.format(

src/main/java/com/dabsquared/gitlabjenkins/webhook/status/BuildPageRedirectAction.java

@@ -4,6 +4,7 @@
 import hudson.model.Run;
 import hudson.util.HttpResponses;
 import java.io.IOException;
+import java.util.Objects;
 import jenkins.model.Jenkins;
 import org.kohsuke.stapler.StaplerResponse;
 
@@ -21,7 +22,8 @@ protected BuildPageRedirectAction(Run<?, ?> build) {
     public void execute(StaplerResponse response) {
         if (build != null) {
             try {
-                response.sendRedirect2(Jenkins.getInstance().getRootUrl() + build.getUrl());
+                response.sendRedirect2(
+                        Objects.requireNonNull(Jenkins.getInstance()).getRootUrl() + build.getUrl());
             } catch (IOException e) {
                 try {
                     response.sendRedirect2(Jenkins.getInstance().getRootUrl() + build.getBuildStatusUrl());

src/main/java/com/dabsquared/gitlabjenkins/workflow/GitLabCommitStatusStep.java

@@ -7,11 +7,7 @@
 import hudson.Extension;
 import hudson.model.Run;
 import hudson.model.TaskListener;
-import java.util.ArrayList;
-import java.util.Collections;
-import java.util.HashSet;
-import java.util.List;
-import java.util.Set;
+import java.util.*;
 import org.apache.commons.lang.StringUtils;
 import org.jenkinsci.plugins.workflow.steps.BodyExecution;
 import org.jenkinsci.plugins.workflow.steps.BodyExecutionCallback;
@@ -132,7 +128,7 @@
 
                             CommitStatusUpdater.updateCommitStatus(
                                     run, getTaskListener(context), state, name, step.builds, step.connection);
-                            context.onFailure(t);
+                            context.onFailure(Objects.requireNonNull(t));
                         }
                     })
                     .start();