message: Fix bug where custom layers could crash.
  Layer.add_weight would crash when called without a dtype or initializer.
diff: @@ -485,7 +485,6 @@ class Layer(checkpointable.CheckpointableBase):
  """
  if dtype is None:
  dtype = self.dtype or backend.floatx()
  - else:
  dtype = dtypes.as_dtype(dtype)
  initializer = initializers.get(initializer)
  regularizer = regularizers.get(regularizer)
  @@ -514,7 +513,7 @@ class Layer(checkpointable.CheckpointableBase):
  # Manage errors in Layer rather than Checkpointable.
  overwrite=True,
  initializer=initializer,
  - dtype=dtypes.as_dtype(dtype),
  + dtype=dtype,
  constraint=constraint,
  trainable=trainable and self.trainable,
  partitioner=partitioner,
  