code: private boolean hasSuperclass(Name es6Class) {
      Node decl = es6Class.getDeclaration().getNode();
      Node classNode = NodeUtil.getRValueOfLValue(decl);
      checkState(classNode.isClass(), classNode);
      Node superclass = classNode.getSecondChild();
  
      return !superclass.isEmpty();
    }
docs: Returns whether the given ES6 class extends something.