NPE when trying to stop scan in background using BackgroundScanner when Bluetooth is disabled

[gryffindor14]

Summary

When Bluetooth is not enabled, calling client.getBackgroundScanner().stopScan(Pending) causes NPE

I assume this is due to BluetoothAdapter#getBluetoothLEScanner() returns null if the BluetoothAdapter is off.

Library version

1.7.0

Preconditions

Bluetooth is on and client returns State.READY for client state

Steps to reproduce actual result

1. startScanningWith background scanner (client.getBackgroundScanner().scanBleDeviceInBackground(settings, filter, PendingIntent)

2. turn off bluetooth

3. stop scanning in background client.getBackgroundScanner().stopScanningInBackground(PendingIntent)

Minimum code snippet reproducing the issue

Logs from the application running with setting RxBleLog.setLogLevel(RxBleLog.VERBOSE)

 Attempt to invoke virtual method 'void android.bluetooth.le.BluetoothLeScanner.stopScan(android.app.PendingIntent)' on a null object reference
        at com.polidea.rxandroidble2.internal.util.RxBleAdapterWrapper.stopLeScan(RxBleAdapterWrapper.java:62)
        at com.polidea.rxandroidble2.internal.scan.BackgroundScannerImpl.stopBackgroundBleScan(BackgroundScannerImpl.java:74)

Actual result

Uncatchable NPE

Expected result

No Exception or BluetoothScanException with Code for Bluetooth being off

[gryffindor14]

Somewhat related, there is a different internal exception when trying to start scanning in the background while bluetooth is disabled.

java.lang.SecurityException: Need BLUETOOTH_PRIVILEGED permission: Neither user 10188 nor current process has android.permission.BLUETOOTH_PRIVILEGED.
        at android.os.Parcel.createException(Parcel.java:1942)
        at android.os.Parcel.readException(Parcel.java:1910)
        at android.os.Parcel.readException(Parcel.java:1860)
        at android.bluetooth.IBluetoothGatt$Stub$Proxy.startScanForIntent(IBluetoothGatt.java:977)
        at android.bluetooth.le.BluetoothLeScanner.startScan(BluetoothLeScanner.java:249)
        at android.bluetooth.le.BluetoothLeScanner.startScan(BluetoothLeScanner.java:166)
        at com.polidea.rxandroidble2.internal.util.RxBleAdapterWrapper.startLeScan(RxBleAdapterWrapper.java:57)
        at com.polidea.rxandroidble2.internal.scan.BackgroundScannerImpl.scanBleDeviceInBackground(BackgroundScannerImpl.java:56)

[dariuszseweryn]

This case should also be handled by the fix on fix/background_scanner_npe branch as it checks if adapter is on. I have created a different issue as potentially a SecurityException may also be thrown when specific settings will be passed to the scan.