I'm experiencing <<null>> results when calling

collection.remove(...)

where the contract says that either a WriteResult is returned or an exception is thrown.

I've tracked this down to DBTCPConnector#_checkWriteError that ends with

WriteResult _checkWriteError( DB db , MyPort mp , DBPort port , WriteConcern concern )
CommandResult e = null;
e = port.runCommand( db , concern.getCommand() );
if ( ! e.hasErr() )
return new WriteResult( e , concern );
e.throwOnError();
return null;
}

if

e.throwOnError();

does not throw an exception ( ok() || !hasErr())

return null;

is returned.