grep: handle deref_tag() returning NULL

deref_tag() can return NULL.  Exit gracefully in that case instead
of blindly dereferencing the return value.

.name shouldn't ever be NULL, but grep_object() handles that case
explicitly, so let's be defensive here as well and show the broken
object's ID if it happens to lack a name after all.

Signed-off-by: René Scharfe <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: rscharfe

builtin/grep.c

@@ -670,6 +670,17 @@ static int grep_objects(struct grep_opt *opt, const struct pathspec *pathspec,
 				     NULL, 0);
 		obj_read_unlock();
 
+		if (!real_obj) {
+			char hex[GIT_MAX_HEXSZ + 1];
+			const char *name = list->objects[i].name;
+
+			if (!name) {
+				oid_to_hex_r(hex, &list->objects[i].item->oid);
+				name = hex;
+			}
+			die(_("invalid object '%s' given."), name);
+		}
+
 		/* load the gitmodules file for this rev */
 		if (recurse_submodules) {
 			submodule_free(opt->repo);