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: I8ed57d5aaed60aaab685fc11a8695e474e60215f
Signed-off-by: Stefan Lay <stefan.lay@sap.com>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

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

 	 */
 	public PullResult call() throws WrongRepositoryStateException,
 			InvalidConfigurationException, DetachedHeadException,
-			InvalidRemoteException, CanceledException {
+			InvalidRemoteException, CanceledException, RefNotFoundException {
 		checkCallable();
 
 		monitor.beginTask(JGitText.get().pullTaskName, 2);
 		} 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,