feat: tuic outbound allow set an empty ALPN array

adapter/outbound/tuic.go

@@ -162,7 +162,7 @@ func NewTuic(option TuicOption) (*Tuic, error) {
 		tlsConfig = tlsC.GetGlobalTLSConfig(tlsConfig)
 	}
 
-	if len(option.ALPN) > 0 {
+	if option.ALPN != nil { // structure's Decode will ensure value not nil when input has value even it was set an empty array
 		tlsConfig.NextProtos = option.ALPN
 	} else {
 		tlsConfig.NextProtos = []string{"h3"}

common/structure/structure.go

@@ -282,6 +282,9 @@ func (d *Decoder) decodeSlice(name string, data any, val reflect.Value) error {
 	}
 
 	valSlice := val
+	// make a new slice with cap(val)==cap(dataVal)
+	// the caller can determine whether the original configuration contains this item by judging whether the value is nil.
+	valSlice = reflect.MakeSlice(valType, 0, dataVal.Len())
 	for i := 0; i < dataVal.Len(); i++ {
 		currentData := dataVal.Index(i).Interface()
 		for valSlice.Len() <= i {