input: Write a python function to convert month names to their corresponding numbers using a dictionary.
  assert month_to_number('January') == 1
  assert month_to_number('April') == 4
  assert month_to_number('December') == 12
output: def month_to_number(month):
      month_dict = {
          'January': 1, 'February': 2, 'March': 3, 'April': 4,
          'May': 5, 'June': 6, 'July': 7, 'August': 8,
          'September': 9, 'October': 10, 'November': 11, 'December': 12
      }
      return month_dict.get(month, None)