title: How to resolve ambiguity when argument is null?
body: <p>Compiling the following code will return <code>The call is ambiguous between the following methods or properties</code> error. How to resolve it since I can't explicitly convert <code>null</code> to any of those classes?</p>
  
  <pre><code>static void Main(string[] args)
  {
      Func(null);
  }
  
  void Func(Class1 a)
  {
  
  }
  
  void Func(Class2 b)
  {
  
  }
  </code></pre>