message: dense attention
diff: @@ -192,10 +192,10 @@ class BaseDenseAttention(Layer):
  raise ValueError(
  '{} layer mask must be a list, '
  'namely [query_mask, value_mask].'.format(class_name))
  - if len(mask) != 2:
  + if len(mask) < 2 or len(mask) > 3:
  raise ValueError(
  - '{} layer mask must be a list of length 2, namely [query_mask, '
  - 'value_mask]. Given length: {}'.format(class_name, len(mask)))
  + '{} layer mask must be a list of length 2 or 3, namely [query_mask, '
  + 'value_mask] or [query_mask, value_mask, key_mask]. Given length: {}'.format(class_name, len(mask)))
  def get_config(self):
  config = {
  