public List<BluetoothGattService> getSupportedGattServices() {
        if (mBluetoothGatt == null) return null;

        return mBluetoothGatt.getServices();
    }
Retrieves a list of supported GATT services on the connected device. This should be
invoked only after {@code BluetoothGatt#discoverServices()} completes successfully.

@return A {@code List} of supported services.
sample_app/src/main/java/uk/co/alt236/btlescan/services/BluetoothLeService.java