code: def clean_nhs_number(x) -> int:
      
      try:
          x = int(x)
          if not is_valid_nhs_number(x):
              raise ValueError
          return x
      except ValueError:
          raise forms.ValidationError(
              "Not a valid NHS number: {}".format(repr(x)))
docs: Returns its parameter as a valid integer NHS number, or raises
      ``django.forms.ValidationError``.