<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def and_evaluator(conditions, leaf_evaluator):
 """ Evaluates a list of conditions as if the evaluator had been applied to each entry and the results AND-ed together. Args: conditions: List of conditions ex: [operand_1, operand_2]. leaf_evaluator: Function which will be called to evaluate leaf condition values. Returns: Boolean: - True if all operands evaluate to True. - False if a single operand evaluates to False. None: if conditions couldn't be evaluated. """

  saw_null_result = False

  for condition in conditions:
    result = evaluate(condition, leaf_evaluator)
    if result is False:
      return False
    if result is None:
      saw_null_result = True

  return None if saw_null_result else True