RxRoom Kotlin: Generated Dao - error: local variable users is accessed from within inner class; needs to be declared final

Question

I'm using RxRoom with Kotlin. In my Dao class If I use this:

@Insert fun insertPaymentRef(paymentRef: PaymentRef): Single<Long>

Or this:

@Insert
fun insertPaymentRef(paymentRef: PaymentRef): Completable

the generated Dao class throws this error

error: local variable paymentRef is accessed from within inner class; needs to be declared final

A sneek peak in the generated class is this:

public Single<Long> insertPaymentRef(PaymentRef paymentRef) {
return Single.fromCallable(new Callable<Long>() {
  @Override
  public Long call() throws Exception {
    __db.beginTransaction();
    try {
      long _result = __insertionAdapterOfPaymentRef.insertAndReturnId(paymentRef);
      __db.setTransactionSuccessful();
      return _result;
    } finally {
      __db.endTransaction();
    }
  }
});

}

The only time I don't get this error is if I only make my insert call like this:

@Insert(onConflict = OnConflictStrategy.REPLACE)
fun insertPaymentRef(paymentRef: PaymentRef)

How do I make the INSERT call work in RxRoom: I've included RxRoom dependency and it works because if I try doing GET calls like this

@Query(PaymentRefDbConstants.QUERY_PAYMENT_REF)
fun getPaymentRef(): Single<PaymentRef>

It works