fix(alerting): fixed evaluation for no_value condition, fixes #7244 (#7247)

* fix(alerting): fixed evaluation for no_value condition, fixes #7244

* feat(alerting): moving null library into grafana, fixing handling on no value / no series

pkg/api/dtos/alerting.go

@@ -3,6 +3,7 @@ package dtos
 import (
 	"time"
 
+	"github.com/grafana/grafana/pkg/components/null"
 	"github.com/grafana/grafana/pkg/components/simplejson"
 	m "github.com/grafana/grafana/pkg/models"
 )
@@ -51,7 +52,7 @@ type AlertTestResultLog struct {
 type EvalMatch struct {
 	Tags   map[string]string `json:"tags,omitempty"`
 	Metric string            `json:"metric"`
-	Value  float64           `json:"value"`
+	Value  null.Float        `json:"value"`
 }
 
 type NotificationTestCommand struct {