var dictionary = new Dictionary<string, string>();
var val = dictionary["mykey"];

string val;
if(dictionary.TryGetValue("mykey", out val))
{
     //The key was found. The value is in val.
}
else
{
    //The key was not present.
}

private void Application_UnhandledException(object sender,
        ApplicationUnhandledExceptionEventArgs e)
    {
         var stackTrace = e.ExceptionObject.StackTrace;
         //Log the stackTrace somewhere.
    }

private void Application_UnhandledException(object sender,
        ApplicationUnhandledExceptionEventArgs e)
    {
         if (e.ExceptionObject is KeyNotFoundException)
         {
             //This was a KeyNotFoundException
         }
    }

public static TValue GetOrThrow<TKey,TValue>(this IDictionary<TKey,TValue> d, TKey key)
{
    try
    {
        return d[key];
    }
    catch(KeyNotFoundException ex)
    {
        throw new KeyNotFoundException(key.ToString()
            + " was not found in the dictionary");
    }
}

var serializedKey = Newtonsoft.Json.JsonConvert.SerializeObject(
    key,
    new JsonSerializerSettings
    {
        //make it easy for humans to read
        Formatting = Formatting.Indented,
        //don't break on loops...that would cause a new error that hides the KeyNotFound!
        ReferenceLoopHandling = ReferenceLoopHandling.Ignore
    });