Does flex not support hashmaps?

I have a Flex object which collects a DTO from the server. All the fields arrive filled in correctly except for the one that is a HashMap. It arrives as null. I've tried giving it a type of both ArrayCollection and Dictionary, but that hasn't fixed it.

Does anyone know if there's an inherent incomaptability between Java HashMap and Flex?

If not, what might I be doing wrong here? I'm looking at my jboss console and I see the data being populated correctly in the server side before delivery to the client. However, as it gets to the client, that field is null. I'm ready to kill myself.