@JsonClass(generateAdapter = true)
data class CommonResponse<T>(val result: T?)

{
    "result": {
        "bar": 1
    }
}

data class Foo(val bar: Int)

interface {

    @Path("/foo")
    fun getFoo(): CommonResponse<Foo>
}

{
  "result": {}
}

{
    "result": {
        "bar": null
    }
}

{
    "result": {}
}