input: Write a function to calculate the square root of a given positive number. Use the math module for computing the square root. If the number is not positive, return None. If the input is 0, return 0.
  assert calculate_square_root(100)==10.0
  assert calculate_square_root(0)==0
  assert calculate_square_root(9)==3.0
  assert calculate_square_root(-1)==None
  assert calculate_square_root(2)==1.4142135623730951
output: def calculate_square_root(number):
      if number < 0:
          return None
      elif number == 0:
          return 0
      else:
          return math.sqrt(number)