input: Write a function to calculate the average of a list of positive integers and output the result. The function should take a list of positive integers as input and return the average value as a float. If the input list is empty or contains non-positive integers, the function should return None.
  
  assert average_of_positive_integers([1, 5, 6, 7, 8]) == 5.4
  assert average_of_positive_integers([]) == None
  assert average_of_positive_integers([1, 0, 5]) == None
  assert average_of_positive_integers([10, 20, 30, 40]) == 25.0
  assert average_of_positive_integers([2, 4, 6, 8]) == 5.0
output: def average_of_positive_integers(lst):
      if not lst or any(x <= 0 for x in lst):
          return None
      return sum(lst) / len(lst)