code: def load(self, value):
          
          if self.property_type is None:
              return value
          elif not isinstance(self.property_type, BaseType):
              raise TypeError('property_type must be schematics BaseType')
          else:
              native_value = self.property_type.to_native(value)
              self.property_type.validate(native_value)
              return native_value
docs: Load a value, converting it to the proper type if validation_type exists.