Mqtt: allow nil/null/none/- as empty values (#17209)

server/mqtt.go

@@ -220,7 +220,7 @@ func (m *MQTT) listenLoadpointSetters(topic string, site site.API, lp loadpoint.
 		}},
 		{"vehicle", func(payload string) error {
 			// https://github.com/evcc-io/evcc/issues/11184 empty payload is swallowed by listener
-			if payload == "-" {
+			if isEmpty(payload) {
 				lp.SetVehicle(nil)
 				return nil
 			}

server/mqtt_setter.go

@@ -1,6 +1,7 @@
 package server
 
 import (
+	"slices"
 	"strconv"
 	"time"
 
@@ -13,6 +14,10 @@ type setter struct {
 	fun   func(string) error
 }
 
+func isEmpty(payload string) bool {
+	return slices.Contains([]string{"-", "nil", "null", "none"}, payload)
+}
+
 func setterFunc[T any](conv func(string) (T, error), set func(T) error) func(string) error {
 	return func(payload string) error {
 		val, err := conv(payload)
@@ -23,20 +28,26 @@ func setterFunc[T any](conv func(string) (T, error), set func(T) error) func(str
 	}
 }
 
+// ptrSetter updates pointer api
+func ptrSetter[T any](conv func(string) (T, error), set func(*T) error) func(string) error {
+	return func(payload string) error {
+		var val *T
+		v, err := conv(payload)
+		if err == nil {
+			val = &v
+		} else if !isEmpty(payload) {
+			return err
+		}
+		return set(val)
+	}
+}
+
 func floatSetter(set func(float64) error) func(string) error {
 	return setterFunc(parseFloat, set)
 }
 
 func floatPtrSetter(set func(*float64) error) func(string) error {
-	return func(s string) error {
-		var val *float64
-		if f, err := parseFloat(s); err == nil {
-			val = &f
-		} else if s != "" {
-			return err
-		}
-		return set(val)
-	}
+	return ptrSetter(parseFloat, set)
 }
 
 func intSetter(set func(int) error) func(string) error {