tree-wide: apply equals-null.cocci

Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/branch.c b/branch.c
index 07a4643..fc49f57 100644
--- a/branch.c
+++ b/branch.c
@@ -302,7 +302,7 @@ void create_branch(struct repository *r,
 		break;
 	}
 
-	if ((commit = lookup_commit_reference(r, &oid)) == NULL)
+	if (!(commit = lookup_commit_reference(r, &oid)))
 		die(_("Not a valid branch point: '%s'."), start_name);
 	oidcpy(&oid, &commit->object.oid);