code: private static ImmutableList<Node> paramNamesOf(Node paramList) {
      checkArgument(paramList.isParamList(), paramList);
  
      ImmutableList.Builder<Node> builder = ImmutableList.builder();
      paramNamesOf(paramList, builder);
      return builder.build();
    }
docs: Returns the NAME parameter nodes of a FUNCTION.
  
  <p>This lookup abstracts over the other legal node types in a PARAM_LIST. It includes only
  those nodes that declare bindings within the function body.