some Discoverers send nil targetgroup so need to check for it when updating a group
some Discoverers send nil targetgroup so need to check for it when updating a group

Conorbro/prometheus,keegancsmith/prometheus,brancz/prometheus,prometheus/prometheus,brancz/prometheus,keegancsmith/prometheus,GoogleCloudPlatform/prometheus,kangwoo/prometheus,kangwoo/prometheus,keegancsmith/prometheus,Gouthamve/prometheus,brancz/prometheus,alileza/prometheus,GoogleCloudPlatform/prometheus,Conorbro/prometheus,prometheus/prometheus,Conorbro/prometheus,amorken/prometheus,alileza/prometheus,amorken/prometheus,kangwoo/prometheus,keegancsmith/prometheus,amorken/prometheus,Gouthamve/prometheus,GoogleCloudPlatform/prometheus,GoogleCloudPlatform/prometheus,GoogleCloudPlatform/prometheus,alileza/prometheus,Conorbro/prometheus,keegancsmith/prometheus,Gouthamve/prometheus,brancz/prometheus,prometheus/prometheus,prometheus/prometheus,amorken/prometheus,kangwoo/prometheus,Gouthamve/prometheus,prometheus/prometheus,alileza/prometheus,alileza/prometheus