How is the missing/mutually exclusive data handled (client ID or taxi stand ID)?

[liangbright]

First, thank you for this open source code, and nice work

"the client called the taxi by phone, then we have a client ID. If the client called the taxi at a taxi stand, then we have a taxi stand ID. Otherwise we have no client identification" so client ID and taxi stand ID seem to be mutually exclusive How is this issue handled?
Also, if there is no client identification, what to do then? I guess use some kind of average embedding values as the inputs to MLP?