Allow nullable parameters

[inaiat]

Like reported by @msramosjr We need check if the value o parameter is nullable before throw exception.

This fix the Minimal.kt example. So we are able to allow nullable fields, like follow code:

@Path("string/{a}")
    data class StringParam(
        @PathParam("A simple String Param") val a: String,
        @QueryParam("Optional String") val optional: String? // Nullable Types are optional
    )

Thank you.

[inaiat]

I tried to push some fix at night, but you was amazing fast! :D