When I use a Map<String,String>, I see that aegis creates a MapType, but the keyType and objectType are both set to ObjectType, and I get a null pointer exception because the ObjectType instance has a null typeMapping. I think I've tracked it down to a method in AbstractTypeCreator: private Type createObjectType() { ObjectType type = new ObjectType(); type.setSchemaType(DefaultTypeMappingRegistry.XSD_ANY); type.setTypeClass(Object.class); return type; } Shouldn't that be setting calling setTypeMapping(tm). I'll submit a patch, but I wanted to make sure this was a problem before I did so