docs: def run(self, value):
          """ Compares value against self.asserted_type.
          Keyword arguments:
          value str -- the value of the associated field to compare
          """
          if self.pass_ and not value.strip():
              return True
  
          if not isinstance(value, type(self.asserted_type)):
              self.error = self.error.format(type(value), self.asserted_type)
              return False
          return True