// `run_metadata`) are valid.
//
//    - `run_options` may be NULL, in which case it will be ignored; or
//      non-NULL, in which case it must point to a `TF_Buffer` containing the
//      serialized representation of a `RunOptions` protocol buffer.
//    - `run_metadata` may be NULL, in which case it will be ignored; or
//      non-NULL, in which case it must point to an empty, freshly allocated

/// the struct pointer (e.g., when a file type is not supported).
///
/// DEFAULT IMPLEMENTATIONS: Some operations have default implementations that
/// TensorFlow uses in case the plugin doesn't supply its own version. An
/// operation `foo` might have a default implementation which uses `bar` and
/// `foobar`. If the plugin supplies `bar` and `foobar`, TensorFlow can use the