code: def not_evaluator(conditions, leaf_evaluator):
    
    if not len(conditions) > 0:
      return None
  
    result = evaluate(conditions[0], leaf_evaluator)
    return None if result is None else not result
docs: Evaluates a list of conditions as if the evaluator had been applied
    to a single entry and NOT was applied to the result.
  
    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 the operand evaluates to False.
        - False if the operand evaluates to True.
      None: if conditions is empty or condition couldn't be evaluated.