Make the choice of NaN values clearer.
Make the choice of NaN values clearer.

Also switch stale nan value to one more suitable for expansion.

prometheus/prometheus,Gouthamve/prometheus,alileza/prometheus,kangwoo/prometheus,amorken/prometheus,amorken/prometheus,amorken/prometheus,prometheus/prometheus,prometheus/prometheus,alileza/prometheus,yanghongkjxy/prometheus,Conorbro/prometheus,prometheus/prometheus,brancz/prometheus,Conorbro/prometheus,keegancsmith/prometheus,kangwoo/prometheus,GoogleCloudPlatform/prometheus,Conorbro/prometheus,AlekSi/prometheus,AlekSi/prometheus,Gouthamve/prometheus,brancz/prometheus,keegancsmith/prometheus,Gouthamve/prometheus,alileza/prometheus,kangwoo/prometheus,Stackdriver/stackdriver-prometheus,GoogleCloudPlatform/prometheus,Stackdriver/stackdriver-prometheus,Stackdriver/stackdriver-prometheus,GoogleCloudPlatform/prometheus,brancz/prometheus,keegancsmith/prometheus,Conorbro/prometheus,Stackdriver/stackdriver-prometheus,yanghongkjxy/prometheus,Gouthamve/prometheus,amorken/prometheus,yanghongkjxy/prometheus,alileza/prometheus,AlekSi/prometheus,keegancsmith/prometheus,prometheus/prometheus,GoogleCloudPlatform/prometheus,GoogleCloudPlatform/prometheus,AlekSi/prometheus,brancz/prometheus,keegancsmith/prometheus,yanghongkjxy/prometheus,kangwoo/prometheus,alileza/prometheus