As reported by a user, It is not possible to write data in a Boolean field using the fluent api (Core). I've debug this a bit and the bytecode generated seems correct:
I think this is a DSE issue but I don't know yet how to provide a test case not using python. The java driver doesn't have this issue since they are using GraphBinary, and not graphson3.
According to the server team, there is no g:Boolean type, so we need to handle the untyped json primitive (true/false).