Fix NullPointer when pulling from a deleted local branch

A checked Exception is thrown instead. 

The reason for throwing an Exception is that the state of the
repository is inconsistent in this case: There is a merge
configuration containing a non-existing local branch. Ideally the
deletion of a local branch should also delete the corresponding
merge configuration.

Bug: 337315
Change-Id: I71e56ffb90e11e6e3c1bbd964ad63972d67990c0
Signed-off-by: Stefan Lay <stefan.lay@sap.com>

org.eclipse.jgit/src/org/eclipse/jgit/api/PullCommand.java

@@ -138,7 +138,7 @@ public class PullCommand extends GitCommand<PullResult> {
 	 */
 	public PullResult call() throws WrongRepositoryStateException,
 			InvalidConfigurationException, DetachedHeadException,
-			InvalidRemoteException, CanceledException {
+			InvalidRemoteException, CanceledException, RefNotFoundException {
 		checkCallable();
 
 		monitor.beginTask(JGitText.get().pullTaskName, 2);
@@ -248,6 +248,9 @@ public class PullCommand extends GitCommand<PullResult> {
 		} else {
 			try {
 				commitToMerge = repo.resolve(remoteBranchName);
+				if (commitToMerge == null)
+					throw new RefNotFoundException(MessageFormat.format(
+							JGitText.get().refNotResolved, remoteBranchName));
 			} catch (IOException e) {
 				throw new JGitInternalException(
 						JGitText.get().exceptionCaughtDuringExecutionOfPullCommand,