Is there a way to ask a Decoder if the next token is a Map?

I have a data structure where there is a field that might be a map or a string. I don't see a way to peek into the decoder and ask it if `readMapSize()` is going to fail. Since there is no support for try/catch in AS, and the reader field in `Decoder` is private, that means I'm stuck. Unless I'm missing something?