Bluetooth - Exception thrown when Bluetooth not enabled on device

[pylapp]

When clicking on the BLE devices-dedicated button in the app, if the Bluetooth is not enabled on this device, the app crashes because of the exception bellow.

2019-08-28 08:34:18.126 8930-8930/com.orange.labs.orangetrainingboxnull.alpha E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.orange.labs.orangetrainingboxnull.alpha, PID: 8930
    java.lang.NullPointerException: Attempt to invoke virtual method 'void android.bluetooth.le.BluetoothLeScanner.startScan(java.util.List, android.bluetooth.le.ScanSettings, android.bluetooth.le.ScanCallback)' on a null object reference
        at com.orange.labs.orangetrainingbox.ui.MainActivity.scanLeDevice(MainActivity.kt:381)
        at com.orange.labs.orangetrainingbox.ui.MainActivity.onOptionsItemSelected(MainActivity.kt:270)
        at android.app.Activity.onMenuItemSelected(Activity.java:3450)
        at androidx.fragment.app.FragmentActivity.onMenuItemSelected(FragmentActivity.java:436)
        at androidx.appcompat.app.AppCompatActivity.onMenuItemSelected(AppCompatActivity.java:196)
        at androidx.appcompat.view.WindowCallbackWrapper.onMenuItemSelected(WindowCallbackWrapper.java:109)
        at androidx.appcompat.view.WindowCallbackWrapper.onMenuItemSelected(WindowCallbackWrapper.java:109)
        at androidx.appcompat.app.ToolbarActionBar$2.onMenuItemClick(ToolbarActionBar.java:64)
        at androidx.appcompat.widget.Toolbar$1.onMenuItemClick(Toolbar.java:204)
        at androidx.appcompat.widget.ActionMenuView$MenuBuilderCallback.onMenuItemSelected(ActionMenuView.java:781)
        at androidx.appcompat.view.menu.MenuBuilder.dispatchMenuItemSelected(MenuBuilder.java:840)
        at androidx.appcompat.view.menu.MenuItemImpl.invoke(MenuItemImpl.java:158)
        at androidx.appcompat.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:991)
        at androidx.appcompat.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:981)
        at androidx.appcompat.widget.ActionMenuView.invokeItem(ActionMenuView.java:625)
        at androidx.appcompat.view.menu.ActionMenuItemView.onClick(ActionMenuItemView.java:151)
        at android.view.View.performClick(View.java:6294)
        at android.view.View$PerformClick.run(View.java:24770)
        at android.os.Handler.handleCallback(Handler.java:790)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:164)
        at android.app.ActivityThread.main(ActivityThread.java:6494)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)