Untracked files should not be included in stash

The previous code stashed untracked files and left them
in the work tree.

Bug: 403282
Change-Id: I71727addb2b55fb8e409cae2b6af8138b1ff7ef1

org.eclipse.jgit.test/tst/org/eclipse/jgit/api/StashCreateCommandTest.java

@@ -88,6 +88,7 @@ public class StashCreateCommandTest extends RepositoryTestCase {
 		git.add().addFilepattern("file.txt").call();
 		head = git.commit().setMessage("add file").call();
 		assertNotNull(head);
+		writeTrashFile("untracked.txt", "content");
 	}
 
 	/**

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

@@ -241,6 +241,7 @@ public class StashCreateCommand extends GitCommand<RevCommit> {
 				MutableObjectId id = new MutableObjectId();
 				List<PathEdit> wtEdits = new ArrayList<PathEdit>();
 				List<String> wtDeletes = new ArrayList<String>();
+				boolean hasChanges = false;
 				do {
 					AbstractTreeIterator headIter = treeWalk.getTree(0,
 							AbstractTreeIterator.class);
@@ -254,9 +255,12 @@ public class StashCreateCommand extends GitCommand<RevCommit> {
 								new UnmergedPathException(
 										indexIter.getDirCacheEntry()));
 					if (wtIter != null) {
-						if (indexIter != null && wtIter.idEqual(indexIter)
-								|| headIter != null
-								&& wtIter.idEqual(headIter))
+						if (indexIter == null && headIter == null)
+							continue;
+						hasChanges = true;
+						if (indexIter != null && wtIter.idEqual(indexIter))
+							continue;
+						if (headIter != null && wtIter.idEqual(headIter))
 							continue;
 						treeWalk.getObjectId(id, 0);
 						final DirCacheEntry entry = new DirCacheEntry(
@@ -278,10 +282,14 @@ public class StashCreateCommand extends GitCommand<RevCommit> {
 							}
 						});
 					}
+					hasChanges = true;
 					if (wtIter == null && headIter != null)
 						wtDeletes.add(treeWalk.getPathString());
 				} while (treeWalk.next());
 
+				if (!hasChanges)
+					return null;
+
 				String branch = Repository.shortenRefName(head.getTarget()
 						.getName());