public static class Ext
{
  public static void Method(this SomeClass bla, params Func<int, int>[] x)
  {    
  }

  public static void Method(this SomeClass bla, params Func<string, int>[] x)
  {
  }
}

public class SomeClass
{
  public void Foo()
  {
    var bla = new SomeClass();
    bla.Method(x=>x);  // 'implicitly converted to type' for this argument is incorrect (try to introduce variable)
  }
}