Optional Undefined Arguments

In GraphQL, input types can be optional which means that the client can either:

• Not specify a value at all
• Send null explictly
• Send the non-null type

Optional input types are represented as nullable parameters in Kotlin

fun optionalInput(value: String?): String? = value

query OptionalInputQuery {
  undefined: optionalInput
  null: optionalInput(value: null)
  foo: optionalInput(value: "foo")
}

By default, if an optional input value is not specified, then the execution engine will set the argument in Kotlin to null. This means that you can not tell, by just the value alone, whether the request did not contain any argument or the client explicitly passed in null.

Instead, you should inspect the DataFetchingEnvironment where you can see if the request had the variable defined and even check parent arguments as well.

fun optionalInput(value: String?, dataFetchingEnvironment: DataFetchingEnvironment): String =
    if (dataFetchingEnvironment.containsArgument("value")) {
        "The value was $value"
    } else {
        "The value was undefined"
    }