int ctl_stream_is_null(CTL_STREAM_t stream);
ctl_stream_is_null returns non-zero if stream is a null stream and zero if it is not a null stream.
It is not enough to compare a stream handle to CTL_STREAM_NULL as the standard streams (CTL_STREAM_STANDARD_INPUT etc) are non-zero stream handled and require unmapping by ctl_stream_unmap to indicate whether they are attched to a non-null stream.
ctl_stream_is_null is thread-safe.