Merge pull request #747 from MarkEWaite/reduce-jgit-portability-gap

Replace JGit 4.5 getRef with findRef or exactRef

Author: MarkEWaite

src/main/java/jenkins/plugins/git/GitSCMFileSystem.java

@@ -113,12 +113,7 @@ protected GitSCMFileSystem(GitClient client, String remote, final String head, @
         cacheEntry = AbstractGitSCMSource.getCacheEntry(remote);
         listener = new LogTaskListener(LOGGER, Level.FINER);
         this.client = client;
-        commitId = rev == null ? invoke(new FSFunction<ObjectId>() {
-            @Override
-            public ObjectId invoke(Repository repository) throws IOException, InterruptedException {
-                return repository.getRef(head).getObjectId();
-            }
-        }) : ObjectId.fromString(rev.getHash());
+        commitId = rev == null ? invoke((Repository repository) -> repository.findRef(head).getObjectId()) : ObjectId.fromString(rev.getHash());
     }
 
     @Override

src/test/java/hudson/plugins/git/GitSCMTest.java

@@ -1603,7 +1603,7 @@ public void testCheckoutToSpecificBranch() throws Exception {
         GitClient gc = Git.with(StreamTaskListener.fromStdout(),null).in(b.getWorkspace()).getClient();
         gc.withRepository(new RepositoryCallback<Void>() {
             public Void invoke(Repository repo, VirtualChannel channel) throws IOException, InterruptedException {
-                Ref head = repo.getRef("HEAD");
+                Ref head = repo.findRef("HEAD");
                 assertTrue("Detached HEAD",head.isSymbolic());
                 Ref t = head.getTarget();
                 assertEquals(t.getName(),"refs/heads/master");