Use HEAD as default ref for RefLogCommand.

This mirrors the default command-line behavior.

Change-Id: I4f819410fa6df3064c560beb3184b61fd7bb1f15
Signed-off-by: Kevin Sawicki <kevin@github.com>

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

 package org.eclipse.jgit.api;
 
 import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.assertNotNull;
 
 import java.util.Collection;
 
+import org.eclipse.jgit.lib.Constants;
+import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.lib.RepositoryTestCase;
 import org.eclipse.jgit.revwalk.RevCommit;
 import org.eclipse.jgit.storage.file.ReflogEntry;
 		writeTrashFile(FILE, "Hello world");
 		git.add().addFilepattern(FILE).call();
 		commit1 = git.commit().setMessage("Initial commit").call();
+		git.checkout().setCreateBranch(true).setName("b1").call();
 		git.rm().addFilepattern(FILE).call();
 		commit2 = git.commit().setMessage("Removed file").call();
-		git.notesAdd().setObjectId(commit1)
-				.setMessage("data").call();
+		git.notesAdd().setObjectId(commit1).setMessage("data").call();
 	}
 
+	/**
+	 * Test getting the HEAD reflog
+	 *
+	 * @throws Exception
+	 */
 	@Test
-	public void testReflog() throws Exception {
+	public void testHeadReflog() throws Exception {
 		Collection<ReflogEntry> reflog = git.reflog().call();
-		assertTrue(reflog.size() == 2);
+		assertNotNull(reflog);
+		assertEquals(3, reflog.size());
 		ReflogEntry[] reflogs = reflog.toArray(new ReflogEntry[reflog.size()]);
-		assertEquals(reflogs[1].getComment(), "commit: Initial commit");
+		assertEquals(reflogs[2].getComment(), "commit: Initial commit");
+		assertEquals(reflogs[2].getNewId(), commit1.getId());
+		assertEquals(reflogs[2].getOldId(), ObjectId.zeroId());
+		assertEquals(reflogs[1].getNewId(), commit1.getId());
+		assertEquals(reflogs[1].getOldId(), commit1.getId());
+		assertEquals(reflogs[0].getComment(), "commit: Removed file");
 		assertEquals(reflogs[0].getNewId(), commit2.getId());
 		assertEquals(reflogs[0].getOldId(), commit1.getId());
 	}
 
+	/**
+	 * Test getting the reflog for an explicit branch
+	 *
+	 * @throws Exception
+	 */
+	@Test
+	public void testBranchReflog() throws Exception {
+		Collection<ReflogEntry> reflog = git.reflog()
+				.setRef(Constants.R_HEADS + "b1").call();
+		assertNotNull(reflog);
+		assertEquals(2, reflog.size());
+		ReflogEntry[] reflogs = reflog.toArray(new ReflogEntry[reflog.size()]);
+		assertEquals(reflogs[0].getComment(), "commit: Removed file");
+		assertEquals(reflogs[0].getNewId(), commit2.getId());
+		assertEquals(reflogs[0].getOldId(), commit1.getId());
+		assertEquals(reflogs[1].getNewId(), commit1.getId());
+		assertEquals(reflogs[1].getOldId(), ObjectId.zeroId());
+	}
 }

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

  */
 public class ReflogCommand extends GitCommand<Collection<ReflogEntry>> {
 
-	private String ref = Constants.R_HEADS + Constants.MASTER;
+	private String ref = Constants.HEAD;
 
 	/**
 	 * @param repo
 
 	/**
 	 * The ref used for the reflog operation. If no ref is set, the default
-	 * value of refs/heads/master will be used.
+	 * value of HEAD will be used.
 	 *
 	 * @param ref
 	 * @return {@code this}