Fixes #10

set.go

@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
+	"math"
 	"strconv"
 	"strings"
 
@@ -74,6 +75,8 @@ func (r *QueryResult) createMetric(facets map[string]interface{}, suffix string)
 
 func setValueForResult(r prometheus.Gauge, v interface{}) error {
 	switch t := v.(type) {
+	case nil:
+		r.Set(math.NaN())
 	case string:
 		f, err := strconv.ParseFloat(t, 64)
 		if err != nil {

set_test.go

@@ -144,3 +144,22 @@ func (opts *testQuerySetOptions) testQuerySet(t *testing.T) {
 	}
 
 }
+
+func TestNilValue(t *testing.T) {
+	(&testQuerySetOptions{
+		q: NewQueryResult(&Query{
+			Name: "nil_metric",
+		}),
+		rec: records{
+			record{
+				"value": nil,
+			},
+		},
+		results: map[string]string{
+			"nil_metric{}": `gauge: <
+  value: nan
+>
+`,
+		},
+	}).testQuerySet(t)
+}