fix: null dynamic attrs

fix-vm/src/instructions/collections.rs

@@ -24,12 +24,13 @@ impl<'gc> crate::Vm<'gc> {
             self.force_slot_to_pc(depth, reader, mc, reader.inst_start_pc())?;
         }
 
-        let mut dyn_keys: SmallVec<[crate::StringId; 2]> = SmallVec::with_capacity(dynamic_count);
+        let mut dyn_keys: SmallVec<[_; 2]> = SmallVec::with_capacity(dynamic_count);
         for i in 0..dynamic_count {
             let depth = dynamic_count - 1 - i;
             let key_val = self.peek_forced(depth);
             let key_sid = match ctx.get_string_id(key_val) {
-                Ok(id) => id,
+                Ok(id) => Some(id),
+                Err(NixType::Null) => None,
                 Err(got) => return self.finish_type_err(NixType::String, got),
             };
             dyn_keys.push(key_sid);
@@ -47,10 +48,12 @@ impl<'gc> crate::Vm<'gc> {
             kv.push((key, val));
         }
 
-        for i in 0..dynamic_count {
+        for key in dyn_keys {
             let val = reader.read_operand_data(ctx).resolve(mc, self);
             let _span_id = reader.read_u32();
-            kv.push((dyn_keys[i], val));
+            if let Some(key) = key {
+                kv.push((key, val))
+            }
         }
 
         kv.sort_by_key(|(k, _)| *k);