map directive in nginx work only in first variant

I try to use map directive. I have 2 vars and if first var exist set it to new var, or if only second var exist, set it to new var. My config:

map "$arg_arg1:$cookie_1" $new_var {
"~^.*:" $arg_arg1;
"~:.*$" $cookie_1;
default "new";
}
Work only in first situation.

nginx