pocketsphinx NullPointerException in onBeginningOfSpeech() but the object is not null

Question

I'm using the below code to start listening on my device for voice commands but as soon as I call SpeechRecognizer.StartListening() I get a NullPointerException.

Here is the full error:

Java.Lang.NullPointerException: Attempt to invoke interface method 'void edu.cmu.pocketsphinx.RecognitionListener.onBeginningOfSpeech()' on a null object reference

as you can see in the code below, I'm checking to make sure my object reference is NOT null. Can anyone shed some light here?

public VoiceRecognizer(MainActivity mainActivity)
        {
            _mainActivity = mainActivity;
            InitializeVoiceRecognizer();
        }

    private async void InitializeVoiceRecognizer()
    {
        await SetupRecognizer();
        SwitchSearch("wakeup");
    }
    private async Task SetupRecognizer()
    {
        Java.Lang.JavaSystem.LoadLibrary("pocketsphinx_jni");
        var config = Edu.Cmu.Pocketsphinx.Decoder.DefaultConfig();
        Java.IO.File filePath = new Java.IO.File(Android.OS.Environment.ExternalStorageDirectory + "/MyApp/voice_recognition");
        speechRecognizer = SpeechRecognizerSetup
            .DefaultSetup()
            .SetAcousticModel(new Java.IO.File(filePath, "en-us-ptm"))
            .SetDictionary(new Java.IO.File(filePath, "cmudict-en-us.dict"))
            .SetKeywordThreshold(1e-45f)
            .SetBoolean("-allphone_ci", true)
            .Recognizer;
        speechRecognizer.AddListener(this);
        speechRecognizer.AddKeywordSearch("wakeup", new Java.IO.File(filePath, "commands.lst"));            
    }
    private void SwitchSearch(string searchName)
    {
        speechRecognizer.Stop();
        if (searchName == "wakeup")
        {
            if (speechRecognizer != null)
                speechRecognizer.StartListening(searchName);
        }
    }

TIA

Edit: Including entire VoiceRecognizer class for more context:

using System;
using System.Threading.Tasks;
using Edu.Cmu.Pocketsphinx;


namespace ExpeditionSpotMobile.Droid.Utilities
{
    public class VoiceRecognizer : Java.Lang.Object,  IRecognitionListener
    {
        private SpeechRecognizer speechRecognizer;
        public IntPtr Handle
        {
            get; set;
        }
        MainActivity _mainActivity;

        public VoiceRecognizer()
        {

        }

        public VoiceRecognizer(MainActivity mainActivity)
        {
            _mainActivity = mainActivity;
            InitializeVoiceRecognizer();
        }

        private async Task InitializeVoiceRecognizer()
        {
            await SetupRecognizer();
            SwitchSearch("wakeup");
        }
        private async Task SetupRecognizer()
        {
            Java.Lang.JavaSystem.LoadLibrary("pocketsphinx_jni");
            var config = Edu.Cmu.Pocketsphinx.Decoder.DefaultConfig();
            Java.IO.File filePath = new Java.IO.File(Android.OS.Environment.ExternalStorageDirectory + "/MyApp/voice_recognition");
            speechRecognizer = SpeechRecognizerSetup
                .DefaultSetup()
                .SetAcousticModel(new Java.IO.File(filePath, "en-us-ptm"))
                .SetDictionary(new Java.IO.File(filePath, "cmudict-en-us.dict"))
                .SetKeywordThreshold(1e-45f)
                .SetBoolean("-allphone_ci", true)
                .Recognizer;
            speechRecognizer.AddListener(this);
            speechRecognizer.AddKeywordSearch("wakeup", new Java.IO.File(filePath, "commands.lst"));            
        }
        private void SwitchSearch(string searchName)
        {
            speechRecognizer.Stop();
            if (searchName == "wakeup")
            {
                if (speechRecognizer != null)
                    speechRecognizer.StartListening(searchName);
            }
        }

        public void Dispose()
        {
            if (speechRecognizer != null)
            {
                speechRecognizer.Cancel();
                speechRecognizer.Shutdown();
            }
        }

        public void OnBeginningOfSpeech()
        {

        }

        public void OnEndOfSpeech()
        {
            if (speechRecognizer.SearchName != "wakeup")
                SwitchSearch("wakeup");
        }

        public void Stop()
        {
            speechRecognizer.Stop();
        }

        public void OnError(Java.Lang.Exception p0)
        {
            //throw new NotImplementedException();
        }

        public void OnPartialResult(Hypothesis hypothesis)
        {
            if (hypothesis == null)
                return;
            SwitchSearch("wakeup");
        }



        public void OnResult(Hypothesis hypothesis)
        {
            if (hypothesis != null)
            {
                string text = hypothesis.Hypstr;
                // do something here
            }
        }

        public void OnTimeout()
        {
            SwitchSearch("wakeup");
        }
    }
}