Как в less использовать mixin с 2-мя параметрами в url?

.pic_url(@folder: define;@name: me) {
	background-image: url("/@{folder}/@{name}.png");
}

.span {
	.pic_url();
}
.span {
	.pic_url(images;some);
}
.span {
	.pic_url(@name: pls);
}
.span {
	.pic_url(@folder: folder;@name: file);
}

.span {
  background-image: url("/define/me.png");
}
.span {
  background-image: url("/images/some.png");
}
.span {
  background-image: url("/define/pls.png");
}
.span {
  background-image: url("/folder/file.png");
}