message: Avoid using variables as booleans (similarly to tensors).
diff: @@ -1267,7 +1267,7 @@ def convolution2d_transpose(
  # Add variables to collections.
  _add_variable_to_collections(layer.kernel, variables_collections, 'weights')
  - if layer.bias:
  + if layer.bias is not None:
  _add_variable_to_collections(layer.bias, variables_collections, 'biases')
  if normalizer_fn is not None:
  @@ -1376,7 +1376,7 @@ def convolution3d_transpose(
  # Add variables to collections.
  _add_variable_to_collections(layer.kernel, variables_collections, 'weights')
  - if layer.bias:
  + if layer.bias is not None:
  _add_variable_to_collections(layer.bias, variables_collections, 'biases')
  if normalizer_fn is not None:
  @@ -2522,7 +2522,7 @@ def separable_convolution2d(
  variables_collections, 'weights')
  _add_variable_to_collections(layer.pointwise_kernel,
  variables_collections, 'weights')
  - if layer.bias:
  + if layer.bias is not None:
  _add_variable_to_collections(layer.bias,
  variables_collections, 'biases')
  