Providing an incorrect query tree filter causes errors

[HeyZoos]

This is a working example.

http://plenar.io/v1/api/sensor-networks/array_of_things_chicago/query?feature=temperature&filter={"col": "temperature", "val": "0", "op": "le"}

This errors.

http://plenar.io/v1/api/sensor-networks/array_of_things_chicago/query?feature=temperature&filter={"prop": "temperature", "val": "0", "op": "le"}