[need help] Strange compiler error when initializing a BLE characteristic

TL;DR it's a compiler bug.

I modified your code as follows so I could reproduce your problem without _profileManager.

class DeviceManager {
    private var _device as Device?;
    private var _service as Service?;
    private var _command as Characteristic?;
    private var _config as Characteristic?;
    private function startFlControl() as Void {
        var device = _device;
        if (null != device) {
            // _service = device.getService(_profileManager.FL_SERVICE);
            _service = device.getService(BluetoothLowEnergy.stringToUuid("fakeuuid"));
            if (null != _service) {
                _config = _service.getCharacteristic(BluetoothLowEnergy.stringToUuid("fakeuuid"));
                _command = _service.getCharacteristic(BluetoothLowEnergy.stringToUuid("fakeuuid"));
            }
        }
    }
}

I got the same compilation error on _command = ...

Seems to be yet another compiler bug. In this case, it seems that the compiler knowledge's that _service != null is only applied to the first line of the if block (_config = ...).

I was able to work around this in a few different ways.

1) This is the worst one lol:

if (null != _service) {
    _config = _service.getCharacteristic(BluetoothLowEnergy.stringToUuid("fakeuuid"));
}
if (null != _service) {
    _command = _service.getCharacteristic(BluetoothLowEnergy.stringToUuid("fakeuuid"));
}

2) A bit better:

if (null != _service) {
    var service = _service;
    _config = service.getCharacteristic(BluetoothLowEnergy.stringToUuid("fakeuuid"));
    _command = service.getCharacteristic(BluetoothLowEnergy.stringToUuid("fakeuuid"));
}

3) This is probably the best way in terms of memory efficiency, as it won't waste memory in additional code at runtime:

(It does leave you open to accidentally casting to the wrong type and causing a run-time error)

if (null != _service) {
    _config = (_service as Service).getCharacteristic(BluetoothLowEnergy.stringToUuid("fakeuuid"));
    _command = (_service as Service).getCharacteristic(BluetoothLowEnergy.stringToUuid("fakeuuid"));
}

I'd say 2) is actually the best approach if you're worried about type-safety. 3) is the best if you care less about type safety and more about saving memory.