 
 }
 
-extension SMMMonitorWindowController {
+extension SMMMonitorWindowController: NSUserInterfaceValidations {
 
     // MARK: General UI
 


import Cocoa

class SMMMonitorWindowController: NSWindowController, NSUserInterfaceValidations {

    @objc init() {
        super.init(window: nil)

    }

    func outlineView(_ outlineView: NSOutlineView, isItemExpandable item: Any) -> Bool {
        if let itemDict = item as? [String:Any] {
            let itemNotExpandableNumber = itemDict["isNotExpandable"] as? NSNumber
            let notExpandable = (itemNotExpandableNumber?.boolValue) ?? false
            return !notExpandable
        }
        else {
            return false
