Location for client using userName

C:\>curl --insecure --user <userid>:<password> --basic https://<ip>/api/v2/location/clients/count -XGET -H "Accept: application/json"

I get: 

{"DeviceCount":{"deviceType":"Wireless_Client","count":16810}}{"DeviceCount":{"deviceType":"Wireless_Client","count":16810}}

C:\>curl --insecure --user <userid>:<password> --basic https://<ip>/api/v2/location/clients?username=<myusername> -XGET -H "Accept: application/json"

Returns nothing!

One reason this will happen is if no device associated with <myusername> is found. To check, if you use the URL

https://<ip>/api/v2/location/clients/

you will see all clients, including the userName field for each device when it is known.  I'd try copying one of these usernames exactly into <myusername> when querying

https://<ip>/api/v2/location/clients?username=<myusername>

and you should get the non-empty response you expect