fix(orm)!: timestamp encoding doesn't handle nil values properly (#12273)

Co-authored-by: Julien Robert <julien@rbrt.fr>

orm/encoding/ormfield/enum.go

@@ -16,7 +16,10 @@ func (e EnumCodec) Decode(r Reader) (protoreflect.Value, error) {
 }
 
 func (e EnumCodec) Encode(value protoreflect.Value, w io.Writer) error {
-	x := value.Enum()
+	var x protoreflect.EnumNumber
+	if value.IsValid() {
+		x = value.Enum()
+	}
 	buf := make([]byte, binary.MaxVarintLen32)
 	n := binary.PutVarint(buf, int64(x))
 	_, err := w.Write(buf[:n])
@@ -24,8 +27,13 @@ func (e EnumCodec) Encode(value protoreflect.Value, w io.Writer) error {
 }
 
 func (e EnumCodec) Compare(v1, v2 protoreflect.Value) int {
-	x := v1.Enum()
-	y := v2.Enum()
+	var x, y protoreflect.EnumNumber
+	if v1.IsValid() {
+		x = v1.Enum()
+	}
+	if v2.IsValid() {
+		y = v2.Enum()
+	}
 	if x == y {
 		return 0
 	} else if x < y {