Avoid sending network Ids if not specified

Specifying network Ids in Basic zone is not allowed. Passing
an empty array of network Ids is not enough as the empty parameter
will still be sent triggering an error. We have to completely avoid
sending the parameter in case the network Ids array is empty.
Merge pull request #1 from petrhosek/avoid-sending-networkid-if-not-specified

Avoid sending network Ids if not specified