         filterLabel.textColor = .disabledControlTextColor
         filterButton.isEnabled = false
 
-        removeObservers()
+        observationTokens = nil
     }
 
 }

        filterLabel.textColor = .windowFrameTextColor
        filterButton.isEnabled = true

        addObservers()
    }

    func windowDidResignMain(_ notification: Notification) {


    // MARK: Observation

    private var observationTokens: [NSKeyValueObservation]?

}

