UML navigatable property not created

[StefanStsc]

I've this part of an UML diagram:

Which generates this code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

public class ButtonManager {

    public ButtonManager() {
    }

    /// <summary>
    /// @param IButton btn
    /// </summary>
    public void addButton(void IButton btn) {
        // TODO implement here
    }

}

The buttons property is missing here that comes from the navigatable property.
I've checked the code and the comparison looks like this:

So it compares the navigatable property to true, but should compare it to the string "navigable".