How to improve ._. unsupported type: interface {}

Dear @dennwc ,

To Allow interface type in writeAsQuads. // TODO(dennwc): support maps (https://github.com/cayleygraph/cayley/blob/f5fd4c04a4ff6460144d6e14eca43aa20538e4ae/schema/writer.go)

What should be done to support interface{} type ?

Could we consider it as String ?

Looking from your advice .

Thank you