[PATCH] git cherry-pick: Add NULL check to sequencer parsing of HEAD

[Neil Horman <nhorman@tuxdriver.com>]

Michael Mueller noted that a feature I recently added failed to check the return
of lookup_commit to ensure that it was not NULL.  I don't think a NULL can
actually happen in the this particular use case, but regardless it seems a good
idea to check.

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
---
 sequencer.c |   11 ++++++++++-
 1 files changed, 10 insertions(+), 1 deletions(-)

diff --git a/sequencer.c b/sequencer.c
index f83cdfd..ad4d781 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -261,7 +261,16 @@ static int is_index_unchanged(void)
 		return error(_("Could not resolve HEAD commit\n"));
 
 	head_commit = lookup_commit(head_sha1);
-	if (!head_commit || parse_commit(head_commit))
+
+	/*
+	 * If head_commit is NULL, just return, as check_commit,
+	 * called from lookup_commit, would have indicated that
+	 * head_commit is not a commit object already.
+	 */
+	if (!head_commit)
+		return;
+
+	if (parse_commit(head_commit))
 		return error(_("could not parse commit %s\n"),
 			     sha1_to_hex(head_commit->object.sha1));
 
-- 
1.7.7.6