Fix "nil map" panic in statistics collection.

models/statistic.go

@@ -5,3 +5,11 @@ type Statistic struct {
 	Tags   map[string]string      `json:"tags"`
 	Values map[string]interface{} `json:"values"`
 }
+
+func NewStatistic(name string) Statistic {
+	return Statistic{
+		Name: name,
+		Tags: make(map[string]string),
+		Values: make(map[string]interface{}),
+	}
+}

monitor/service.go

@@ -210,9 +210,7 @@ func (m *Monitor) Statistics(tags map[string]string) ([]*Statistic, error) {
 		}
 
 		statistic := &Statistic{
-			Statistic: models.Statistic{
-				Values: make(map[string]interface{}),
-			},
+			Statistic: models.NewStatistic(""),
 		}
 
 		// Add any supplied tags.
@@ -277,10 +275,7 @@ func (m *Monitor) Statistics(tags map[string]string) ([]*Statistic, error) {
 
 	// Add Go memstats.
 	statistic := &Statistic{
-		Statistic: models.Statistic{
-			Name:   "runtime",
-			Values: make(map[string]interface{}),
-		},
+		Statistic: models.NewStatistic("runtime"),
 	}
 
 	// Add any supplied tags to Go memstats