docs: def _validate_target(self, y):
          """
          Raises a value error if the target is not a classification target.
          """
          # Ignore None values
          if y is None:
              return
  
          y_type = type_of_target(y)
          if y_type not in ("binary", "multiclass"):
              raise YellowbrickValueError((
                  "'{}' target type not supported, only binary and multiclass"
              ).format(y_type))