Fix return nil addr in conn

transport/v2raygrpc/conn.go

@@ -7,6 +7,7 @@ import (
 
 	"github.com/sagernet/sing-box/common/baderror"
 	"github.com/sagernet/sing/common"
+	M "github.com/sagernet/sing/common/metadata"
 	"github.com/sagernet/sing/common/rw"
 )
 
@@ -62,11 +63,11 @@ func (c *GRPCConn) Close() error {
 }
 
 func (c *GRPCConn) LocalAddr() net.Addr {
-	return nil
+	return M.Socksaddr{}
 }
 
 func (c *GRPCConn) RemoteAddr() net.Addr {
-	return nil
+	return M.Socksaddr{}
 }
 
 func (c *GRPCConn) SetDeadline(t time.Time) error {