JSON objects (hashes) only support string keys, so we should raise an error for anything not string-like. I judge symbols string-like, so we could indeed convert those. For expected behaviour when using the deserialized hash in `#perform`, I suggest we use a `HashWithIndifferentAccess`. 

Note that `:daily` as a value isn't allowed right now anyway since we can't know whether a string sent over the wire was actually meant to be a symbol. 

I'd only make an exception for hash keys because indifferent access makes everything work as expected, no matter if the keys were intended as strings or symbols.