When starting 10.2 with server-id=0 or without server-id configured, following note is printed:
2017-05-01 8:26:22 140643309708800 [Warning] option 'server_id': unsigned value 0 adjusted to 1
And the value indeed becomes '1'
According to documentation '0' is valid value for server_id indicating that this server is not intended to be part of replication.
Thus either 0 should preserve as valid value or documentation must be changed.