500 error when I try to load user list

[Enrico Piccini]

Try this query:

http://api-dev.udemi.org/v1/users/?latitude_south=44.0450978087067&latitude_north=44.32477412372649&longitude_west=11.835614653515677&longitude_east=12.750226469921927&_=1446284441531

[André Palma]

This issue was caused when users didn't had any counters associated. This is now fixed.