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 ?