IDevice.ReadRssi() throws NullReferenceException

I am playing around with the plugin a bit and ran into this issue with calling ReadRssi() on an IDevice instance.

What I am doing is basically, scan for devices, select one of them and show details about it.

On that selected IDevice instance I do:

_device?.ReadRssi();

This throws the following exception:

05-04 10:43:20.080 E/mono-rt (20530): [ERROR] FATAL UNHANDLED EXCEPTION: System.NullReferenceException: Object reference not set to an instance of an object.
05-04 10:43:20.080 E/mono-rt (20530):   at MvvmCross.Plugins.BLE.Droid.Bluetooth.LE.Device.ReadRssi () [0x00000] in c:\Users\sead\Documents\GitHub\MvvmCross-BluetoothLE\Source\MvvmCross.Plugins.BLE.Droid\Bluetooth\LE\Device.cs:264 
05-04 10:43:20.080 E/mono-rt (20530):   at com.bksv.ems.sxuble.ViewModels.DeviceDetailsViewModel.StartData () [0x00031] in C:\Users\Tomasz\Documents\Visual Studio 2015\Projects\SXUBLE\SXUBLE\ViewModels\DeviceDetailsViewModel.cs:90 
05-04 10:43:20.080 E/mono-rt (20530):   at com.bksv.ems.sxuble.droid.Views.DeviceDetailsView.OnResume () [0x00008] in C:\Users\Tomasz\Documents\Visual Studio 2015\Projects\SXUBLE\SXUBLE.Droid\Views\DeviceDetailsView.cs:22 
05-04 10:43:20.080 E/mono-rt (20530):   at Android.App.Activity.n_OnResume (IntPtr jnienv, IntPtr native__this) [0x00009] in /Users/builder/data/lanes/2923/b4be22e9/source/monodroid/src/Mono.Android/platforms/android-23/src/generated/Android.App.Activity.cs:3920 
05-04 10:43:20.080 E/mono-rt (20530):   at (wrapper dynamic-method) System.Object:ec6c167c-6312-4270-86db-3b0ff9ed091e (intptr,intptr)

Looking at the line it throws at: https://github.com/xabre/xamarin-bluetooth-le/blob/master/Source/MvvmCross.Plugins.BLE.Droid/Bluetooth/LE/Device.cs#L264 it could seem like the _gattCallback is null for some reason.

[Cheesebaron]

I guess XML docs would be a good place to document this. Or a small wiki walking this through.

[Cheesebaron]

Yes, it is good now 👍