list view is unable to display data from cloud firestore - xamarin.forms

Question

Here is my code behind
IIdentifiable is a interface that has Id as property.
I am getting a nullrefrence exceptions while extracting data.
public abstract class SalonService<T> : ISalonService<T> where T : IIdentifiable
{
public Task<T> GetSalonAsync(string id)
{
var tcs = new TaskCompletionSource<T>();
FirebaseFirestore.Instance
.Collection("salons")
.Document(id)
.Get()
.AddOnCompleteListener(new OnDocumentCompleteListener<T>(tcs));
return tcs.Task;
}
public Task<IList<T>> GetSalonsAsync()
{
var tcs = new TaskCompletionSource<IList<T>>();
var list = new List<T>();
FirebaseFirestore.Instance
.Collection("salons")
.Get()
.AddOnCompleteListener(new OnCollectionCompleteListener<T>(tcs));
return tcs.Task;
}
}
And the service listeners for collection of data
public class OnCollectionCompleteListener<T> : Java.Lang.Object, IOnCompleteListener
where T : IIdentifiable
{
private System.Threading.Tasks.TaskCompletionSource<IList<T>> _tcs;
public OnCollectionCompleteListener(System.Threading.Tasks.TaskCompletionSource<IList<T>> tcs)
{
_tcs = tcs;
}
public void OnComplete(Task task)
{
if (task.IsSuccessful)
{
var docsObj = task.Result;
if (docsObj is QuerySnapshot docs)
{
_tcs.TrySetResult(docs.Convert<T>());
}
}
}
}
Service listener to display document
public class OnDocumentCompleteListener<T> : Java.Lang.Object, IOnCompleteListener
where T : IIdentifiable
{
private TaskCompletionSource<T> _tcs;
public OnDocumentCompleteListener(TaskCompletionSource<T> tcs)
{
_tcs = tcs;
}
public void OnComplete(Task task)
{
if (task.IsSuccessful)
{
var docObj = task.Result;
if (docObj is DocumentSnapshot docRef)
{
_tcs.TrySetResult(docRef.Convert<T>());
return;
}
}
// something went wrong
_tcs.TrySetResult(default);
}
}
The Document extension as well
public static class DocumentReferenceExtensions
{
public static T Convert<T>(this DocumentSnapshot doc) where T : IIdentifiable
{
try
{
var jsonStr = Newtonsoft.Json.JsonConvert.SerializeObject(doc.Data.ToDictionary());
var item = Newtonsoft.Json.JsonConvert.DeserializeObject<T>(jsonStr);
item.Id = doc.Id;
return item;
}
catch (Exception)
{
System.Diagnostics.Debug.WriteLine("EXCEPTION THROWN");
}
return default;
}
public static List<T> Convert<T>(this QuerySnapshot docs) where T : IIdentifiable
{
var list = new List<T>();
foreach (var doc in docs.Documents)
{
list.Add(doc.Convert<T>());
}
return list;
}
}
Please let me know what am I missing? I am stuck here