opt: Add missing NULL check in visit_shallow()

visit_shallow() should propagate NULL, but look_up_visitor()
dereferences expr to know which visitor to return.

1 files changed, 5 insertions, 1 deletions

diff --git a/src/opt.c b/src/opt.c
index ffc795b..883d598 100644
--- a/src/opt.c
+++ b/src/opt.c
@@ -947,8 +947,12 @@ static struct bfs_expr *visit_shallow(struct bfs_opt *opt, struct bfs_expr *expr
 		expr = general(opt, expr, visitor);
 	}
 
+	if (!expr) {
+		return NULL;
+	}
+
 	visit_fn *specific = look_up_visitor(expr, visitor->table);
-	if (expr && specific) {
+	if (specific) {
 		expr = specific(opt, expr, visitor);
 	}