Mechanism to pass equivalent of no optional argument explicitly

[nguerrera]

Say you have a decorator with two optional string parameters:

extern dec test(target: unknown, arg1?: string, arg2?: string);

How do you pass arg2 without passing arg1? @test(null, "hello") doesn't compile and shouldn't compile and even if it did, it would be observably different to the JS implementation than the undefined value it gets when the optional args are not passed at all. Do we need undefined in TypeSpec? I have long hoped we didn't but this seems like a gap.