For passing references we would need to know at the time the parameters are prepared, before actually invoking the function, that references are expected. That can only be done by defining it in the signature ... but when doing that func_get_args() is rather useless - the only case would be an undefined number of reference parameters which can be simulated by using an array of references as parameter ... but then again: There's barely any reason for using references these days in PHP.

I usually prefer to check if the variable(s) are empty before calling indexes on them. Or make it able to func_get_args() to pass variables by reference, or extend isset() and empty() to check multiple items. If the parameter is not a reference, PHP gives a undefined index notice.