title: Null reference in WPF
body: <p>I need help with an annoying bug that I can't seem to overcome.</p>
  
  <p>In my work I have a large <code>WPF</code>/<code>C#</code> program and sometimes when you login there is an exception thrown, a <code>null</code> reference exception at <code>System.Windows.Data.BindingExpression.IsValidValueForUpdate</code>.</p>
  
  <p>The exception is only caught in the <code>app.xaml.cs</code> as a <code>DispatcherUnhandledExceptionEventArgs</code>
  and when I look at the data of the exception it contains a key that is an object (not specific object) and the value of the key is null.</p>
  
  <p>How do I even start and find the problem? I read online multiple things and I put some code in comment but still can't find what is wrong.  If anyone has advice how to debug this kind of problem it would be much appreciated. 
  Thanks in advance</p>