what is the different process between the parameter domain is null and empty string.

Hello,

Recently I use the SmbFile.connect to check if the Authentication is
successful, in Android, using JCIFS.

The authentication test runs in two remote machines, the two remote
machines are inside different domain server.
I call SmbFile.connect to access the two remote machines, when the
parameter of domain is null, one of the two remote machine can access
successfully,
the other can not access, SmbFile.connect return connect fail:Logon
failure: unknown user name or bad password.
However when the parameter of domain is empty string, the two remote
machines can access succesfully.

 I see when domain is null then use the "?" to replace in the source
 code,but
 I don't know that whether there will be special process about the "?" .

 If possible, can you tell me what is the different process between the
 parameter domain is null and empty string.

 Thanks a lot.