rt: Null check in walk_obj_contents. Prevents marking from crashing when calling object constructors.

1 files changed, 2 insertions, 0 deletions

diff --git a/src/rt/rust_shape.h b/src/rt/rust_shape.h
index e8a30d5874a..060dd7fed40 100644
--- a/src/rt/rust_shape.h
+++ b/src/rt/rust_shape.h
@@ -903,6 +903,8 @@ data<T,U>::walk_obj_contents(bool align, ptr &dp) {
     type_desc *subtydesc =
         *reinterpret_cast<type_desc **>(box_ptr + sizeof(void *));
     ptr obj_closure_dp(box_ptr + sizeof(void *));
+    if (!box_ptr)   // Null check.
+        return;
 
     arena arena;
     type_param *params = type_param::from_obj_shape(subtydesc->shape,