Best way for handle missing args in REST interface in vibed

[Suliman via Digitalmars-d-learn]

I am doing REST interface with vibed. And thinking about handling 
errors, if users forgot to pass all expected args in function.

For example:
foo(int x, int y) // get request
{

}

/api/foo?x=111

And if user is forgot to pass `y` we will get error in the 
browser. What is the right way to handle curch cases?

Wrap is with try-catch looks wrong.