Merge branch 'js/check-null-from-read-object-file'

The code paths that call repo_read_object_file() have been
tightened to react to errors.

* js/check-null-from-read-object-file:
  Always check the return value of `repo_read_object_file()`

builtin/grep.c

@@ -571,6 +571,8 @@ static int grep_cache(struct grep_opt *opt,
 
 			data = repo_read_object_file(the_repository, &ce->oid,
 						     &type, &size);
+			if (!data)
+				die(_("unable to read tree %s"), oid_to_hex(&ce->oid));
 			init_tree_desc(&tree, data, size);
 
 			hit |= grep_tree(opt, pathspec, &tree, &name, 0, 0);