Recording kinda working but not quite

src/PropertyList.php

@@ -26,8 +26,9 @@ class PropertyList implements ArrayAccess, IteratorAggregate, Countable
 
     public function offsetGet($key)
     {
-        if (!array_key_exist($key, $this->properties)) {
-            throw new InvalidArgumentException("No such property: {$key}");
+        if (!array_key_exists($key, $this->properties)) {
+            return null;
+            // throw new InvalidArgumentException("No such property: {$key}");
         }
         return $this->properties[$key];
     }