Xamarin Forms overriding OnAppearing causes app to crash - xamarin.forms

Question

I am trying to do a simple override and load some data when my page loads, I am using the following code in the code behind page.
namespace XYZ
{
public partial class MainPage : ContentPage
{
private Label results;
private Label groupResults;
public MainPage()
{
InitializeComponent();
results = new Label();
groupResults = new Label();
}
protected override void OnAppearing()
{
base.OnAppearing();
storeIdTxt.Text = Settings.StoreIdSetting;
}
}
}
If I uncomment the override things works just fine, the error I am getting seems to be a generic one attached here
my settings class is fairly simple as follows
using System;
using System.Collections.Generic;
using System.Text;
using Plugin.Settings;
using Plugin.Settings.Abstractions;
namespace NWMPosNG.Helpers
{
/// <summary>
/// This is the Settings static class that can be used in your Core solution or in any
/// of your client applications. All settings are laid out the same exact way with getters
/// and setters.
/// </summary>
public static class Settings
{
private static ISettings AppSettings
{
get
{
return CrossSettings.Current;
}
}
#region Setting Constants
private const string SettingsKey = "settings_key";
private static readonly string SettingsDefault = string.Empty;
private const string StoreId = null;
private static readonly string StoreIdDefault = "0";
#endregion
public static string GeneralSettings
{
get
{
return AppSettings.GetValueOrDefault(SettingsKey, SettingsDefault);
}
set
{
AppSettings.AddOrUpdateValue(SettingsKey, value);
}
}
public static string StoreIdSetting
{
get
{
return AppSettings.GetValueOrDefault(StoreId, StoreIdDefault);
}
set
{
AppSettings.AddOrUpdateValue(StoreId, value);
}
}
}
}
I narrowed down the issue to when I access the saved data using
storeIdTxt.Text = Settings.StoreIdSetting;
But I don't understand why that causes the crash.

Answer 1

You are using the Settings Plugin from James Montemagno. Which is pretty much a KeyValuePair that is stored on the local device across sessions.
In your case:
AppSettings.GetValueOrDefault(StoreId, StoreIdDefault);
Translates to:
AppSettings.GetValueOrDefault(null, "0");
Which crashes because 'null' can't be a key. That's why setting the key (StoreId) prevents the crash from happening.

Answer 2

This line was the culprit
private const string StoreId = null;
I don't really understand why but setting this to a non NULL value makes the crash go away