set(item?: FirebaseOperation, value?: Object): firebase.Promise<void> {
    if (!value){
      throw new Error("The set method requires a defined non-null value. Use remove method to delete instead.");
    }
    // if no item parameter is provided, destructively replace the whole list with value
    if (!item) {
      return this.$ref.ref.set(value);
    }
    return this._checkOperationCases(item, {
      stringCase: () => this.$ref.ref.child(<string>item).set(value),
      firebaseCase: () => (<firebase.database.Reference>item).set(value),
      snapshotCase: () => (<firebase.database.DataSnapshot>item).ref.set(value),
      unwrappedSnapshotCase: () => this.$ref.ref.child((<AFUnwrappedDataSnapshot>item).$key).set(value)
    });
  }