How invoke method for a method by default value for parameters by reflection

I have need to invoke a method by default value parameters. It has a TargetParameterCountException by this message : Parameter count mismatch

var methodName = "MyMethod";
var params = new[] { "Param 1"};

var method = typeof(MyService).GetMethod(methodName, BindingFlags.Instance | BindingFlags.NonPublic);
method.Invoke(method.IsStatic ? null : this, params);

private void MyMethod(string param1, string param2 = null)
{
}

Why? How can I invoke this method by reflection for default value for parameters?