What does invoke do here ?

[jashgopani]

override fun onCharacteristicChanged(gatt: BluetoothGatt, characteristic: BluetoothGattCharacteristic) {
        super.onCharacteristicChanged(gatt, characteristic)
        if (notifyListeners.containsKey(characteristic.uuid)) {
            notifyListeners[characteristic.uuid]?.invoke(characteristic.value)
        }
    }

In the above code , what does notifyListeners[characteristic.uuid]?.invoke(characteristic.value) do ?