Optional for command parameter

[ikfir]

An example

@SubCommand("<?string>")
public void example(Optional<String> optStr) {
  // Do something
}

it also can just give you a null

@SubCommand("<?string>")
public void example(String str) { // String could be null
  // Do something
}

We have a few edge cases

1. no parameter: should put null or skip
2. parameter not match parser: should put null or skip

Should we make it dynamic by given multiple way to request optional or just include both cases?