_connectSlotMixin() {
    super._connectSlotMixin();
    if (this._isPrivateSlot(this._currencyDisplayNodeSlot)) {
      this._onCurrencyChanged({ currency: this.currency || null });
    }
  }
Upon connecting slot mixin, we should check if
the required slot was created by the slot mixin,
and if so, we should execute the currency changed flow
which evaluates whether the slot node should be
removed for invalid currencies