message: ValueError raised when weights is a None object
  Previously: raise ValueError when weights list is empty.
  Now: raise ValueError when weights list does not exist or is empty.
diff: @@ -1803,12 +1803,12 @@ class Layer(module.Module, version_utils.LayerVersionSelector):
  else:
  expected_num_weights += 1
  - if expected_num_weights != len(weights):
  + if not weights or expected_num_weights != len(weights):
  raise ValueError(
  'You called `set_weights(weights)` on layer "%s" '
  'with a weight list of length %s, but the layer was '
  'expecting %s weights. Provided weights: %s...' %
  - (self.name, len(weights), expected_num_weights, str(weights)[:50]))
  + (self.name, len(weights) if weights else 0, expected_num_weights, str(weights)[:50]))
  weight_index = 0
  weight_value_tuples = []
  