code: def check_type_of_param_list_elements(param_list):
      
      try:
          assert isinstance(param_list[0], np.ndarray)
          assert all([(x is None or isinstance(x, np.ndarray))
                      for x in param_list])
      except AssertionError:
          msg = "param_list[0] must be a numpy array."
          msg_2 = "All other elements must be numpy arrays or None."
          total_msg = msg + "\n" + msg_2
          raise TypeError(total_msg)
  
      return None
docs: Ensures that all elements of param_list are ndarrays or None. Raises a
      helpful ValueError if otherwise.