Null LOCation fields in nslc info should be complimentary converted to "--" #17
Description
There's lots of "ughs" in seismology with respect to "--" vs "" for location. If we can, we should try to help users by gracefully allowing active Nulls via "" == "--" e.g.:
squac_client.v1_0_nslc_channels_list(network='UW', location='')
vs
squac_client.v1_0_nslc_channels_list(network='UW')
The first with location='' should only return location="--", while the second one should return all location fields.
I could be missing something about this one so feel free to ignore it if there's other confusions it could add.