Generate method return non optional fragment type in response-based codegen

[sonatard]

Use case

fragment StorefrontErrorMessage on DisplayableError {
    field
    message
}

mutation XUpdate($input: XInput!) {
    xrUpdate(x: $input,) {
        userErrors {
            ... StorefrontErrorMessage
        }
    }
}

fun create(storefrontErrorMessages: List<StorefrontErrorMessage>?): Throwable? { }

I need to use mapNotNull, but since it will never actually be null, I want to use map instead.

 StorefrontApiError.create(
            storefrontErrorMessages =
                xUpdate?.userErrors
-                    ?.mapNotNull { it.storefrontErrorMessage() }
+                    ?.map { it.storefrontErrorMessage() }
        )

Describe the solution you'd like

When it is not a union or interface, create a method that returns a non optional fragment type.