Treat CloneCommand.setRemote(null) as setRemote("origin")

A non-bare clone command with null remote produces a
NullPointerException when trying to produce a refspec to fetch against.

In a bare repository, a null remote name is accepted by mistake,
producing a configuration with items like 'remote.url' instead of
'remote.<remote>.url'.  This was never meant to work.

Instead, let's make setRemote(null) undo any previous setRemote calls
and re-set the remote name to DEFAULT_REMOTE, imitating C git clone's
--no-origin option.

While we're here, add some tests for setRemote working normally.

Change-Id: I76f502da5e677df501d3ef387e7f61f42a7ca238
Signed-off-by: Jonathan Nieder <jrn@google.com>

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

@@ -202,6 +202,66 @@ public class CloneCommandTest extends RepositoryTestCase {
 				fetchRefSpec(git2.getRepository()));
 	}
 
+	@Test
+	public void testCloneRepositoryCustomRemote() throws Exception {
+		File directory = createTempDirectory("testCloneRemoteUpstream");
+		CloneCommand command = Git.cloneRepository();
+		command.setDirectory(directory);
+		command.setRemote("upstream");
+		command.setURI(fileUri());
+		Git git2 = command.call();
+		addRepoToClose(git2.getRepository());
+		assertEquals("+refs/heads/*:refs/remotes/upstream/*",
+				git2.getRepository()
+					.getConfig()
+					.getStringList("remote", "upstream",
+							"fetch")[0]);
+		assertEquals("upstream",
+				git2.getRepository()
+					.getConfig()
+					.getString("branch", "test", "remote"));
+		assertEquals(db.resolve("test"),
+				git2.getRepository().resolve("upstream/test"));
+	}
+
+	@Test
+	public void testBareCloneRepositoryCustomRemote() throws Exception {
+		File directory = createTempDirectory("testCloneRemoteUpstream_bare");
+		CloneCommand command = Git.cloneRepository();
+		command.setBare(true);
+		command.setDirectory(directory);
+		command.setRemote("upstream");
+		command.setURI(fileUri());
+		Git git2 = command.call();
+		addRepoToClose(git2.getRepository());
+		assertEquals("+refs/heads/*:refs/heads/*",
+				git2.getRepository()
+					.getConfig()
+					.getStringList("remote", "upstream",
+							"fetch")[0]);
+		assertEquals("upstream",
+				git2.getRepository()
+					.getConfig()
+					.getString("branch", "test", "remote"));
+		assertNull(git2.getRepository().resolve("upstream/test"));
+	}
+
+	@Test
+	public void testBareCloneRepositoryNullRemote() throws Exception {
+		File directory = createTempDirectory("testCloneRemoteNull_bare");
+		CloneCommand command = Git.cloneRepository();
+		command.setBare(true);
+		command.setDirectory(directory);
+		command.setRemote(null);
+		command.setURI(fileUri());
+		Git git2 = command.call();
+		addRepoToClose(git2.getRepository());
+		assertEquals("+refs/heads/*:refs/heads/*", git2.getRepository()
+				.getConfig().getStringList("remote", "origin", "fetch")[0]);
+		assertEquals("origin", git2.getRepository().getConfig()
+				.getString("branch", "test", "remote"));
+	}
+
 	public static RefSpec fetchRefSpec(Repository r) throws URISyntaxException {
 		RemoteConfig remoteConfig =
 				new RemoteConfig(r.getConfig(), Constants.DEFAULT_REMOTE_NAME);

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

@@ -403,10 +403,14 @@ public class CloneCommand extends TransportCommand<CloneCommand, Git> {
 	 *
 	 * @see Constants#DEFAULT_REMOTE_NAME
 	 * @param remote
-	 *            name that keeps track of the upstream repository
+	 *            name that keeps track of the upstream repository.
+	 *            {@code null} means to use DEFAULT_REMOTE_NAME.
 	 * @return this instance
 	 */
 	public CloneCommand setRemote(String remote) {
+		if (remote == null) {
+			remote = Constants.DEFAULT_REMOTE_NAME;
+		}
 		this.remote = remote;
 		return this;
 	}