http sender fails if groupGauges is set to false

[colomb001]

While doing some testing for a move from davidB's metrics-influxdb to this library, I encountered some peculiar behavior. I'm using the InfluxDbHttpSender with the InfluxDbReporter. If a gauge is registered against the registry and groupGauges is set to false, I get a HTTP response code of 400. If I set groupGauges to true, the metric is sent correctly.

metrics-core 4.0.2
Influxdb 1.5.1
drop wizard-metrics-influxdb 1.2.2