Merge pull request #841 from breed808/thermal_empty

Thermalzone: return error on empty result

collector/thermalzone.go

@@ -1,6 +1,8 @@
 package collector
 
 import (
+	"errors"
+
 	"github.com/StackExchange/wmi"
 	"github.com/prometheus-community/windows_exporter/log"
 	"github.com/prometheus/client_golang/prometheus"
@@ -75,6 +77,11 @@ func (c *thermalZoneCollector) collect(ch chan<- prometheus.Metric) (*prometheus
 		return nil, err
 	}
 
+	// ThermalZone collector has been known to 'successfully' return an empty result.
+	if len(dst) == 0 {
+		return nil, errors.New("Empty results set for collector")
+	}
+
 	for _, info := range dst {
 		//Divide by 10 and subtract 273.15 to convert decikelvin to celsius
 		ch <- prometheus.MustNewConstMetric(