Fix null transmission

ui/amqp_test.go

@@ -33,6 +33,18 @@ func TestNewAmqp(t *testing.T) {
 
 		client.Consume(event)
 
+		event = &yabl.Event{
+			Tag:        &tag,
+			Field:      &field,
+			ActionName: &action,
+			Object:     nil,
+			//unit:       3,
+			Updated: &now,
+			Value:   nil,
+		}
+
+		client.Consume(event)
+
 		client.Stop()
 	})
 

yabl/strings.go

@@ -217,19 +217,24 @@ func (c ConnectedOut8bitType) String() string {
 }
 
 func (u *Event) MarshalJSON() ([]byte, error) {
+	var val *string
+	if u.Value != nil {
+		s := fmt.Sprintf("%v", u.Value)
+		val = &s
+	}
 	return json.Marshal(struct {
 		Host       *string
 		Unit       uint
 		ActionName *AName
 		Field      *FName
 		Updated    *time.Time
-		Value      string
+		Value      *string `json:"Value,omitempty"`
 	}{
 		Host:       u.Tag,
 		Unit:       u.GetUnitId(),
 		ActionName: u.ActionName,
 		Field:      u.Field,
 		Updated:    u.Updated,
-		Value:      fmt.Sprintf("%v", u.Value),
+		Value:      val,
 	})
 }