Normative: Use proper default constructor with class extends null

spec.html

@@ -19016,7 +19016,7 @@ <h1>Runtime Semantics: ClassDefinitionEvaluation</h1>
         1. If |ClassBody_opt| is not present, let _constructor_ be ~empty~.
         1. Else, let _constructor_ be ConstructorMethod of |ClassBody|.
         1. If _constructor_ is ~empty~, then
-          1. If |ClassHeritage_opt| is present, then
+          1. If |ClassHeritage_opt| is present and _protoParent_ is not *null*, then
             1. Let _constructor_ be the result of parsing the source text
               <pre><code class="javascript">constructor(... args){ super (...args);}</code></pre>
               using the syntactic grammar with the goal symbol |MethodDefinition|.