builtin/checkout: handle -B from detached HEAD correctly

Ensure that strcmp() isn't called when head is null.

Previously we were getting segfaults when checkout -B was done from a
detached HEAD.

Signed-off-by: Tay Ray Chuan <rctay89@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/branch.c b/branch.c
index 2ab42aaf4..93dc866f8 100644
--- a/branch.c
+++ b/branch.c
@@ -159,7 +159,7 @@ void create_branch(const char *head,
 			dont_change_ref = 1;
 		else if (!force)
 			die("A branch named '%s' already exists.", name);
-		else if (!is_bare_repository() && !strcmp(head, name))
+		else if (!is_bare_repository() && head && !strcmp(head, name))
 			die("Cannot force update the current branch.");
 		forcing = 1;
 	}