Delegate for NSOutlineView that allows specifying an item right-click menu.

OutlineViewDelegate.swift

import AppKit

protocol OutlineViewDelegate {

    func outlineView(outlineView: NSOutlineView, menuForItem item: Any) -> NSMenu?
}

extension OutlineViewDelegate {

    func outlineView(outlineView: NSOutlineView, menuForItem item: Any) -> NSMenu? {
        return nil
    }
}