onChange Tabbed Panel, got an error in my Window Panel.

I have a problem with my window panel, when i close the panel in after effects i got this error NULL IS NOT AN OBJECT in this line: switch(selectedTab.selection.text) how can i resolve that?

The thing is that i have this cases to call my TabbedPanel with the different tab names, but when i close all the window panel i got that error.

// FUNCIONES EL TABBED PANEL
myPanel.grp.myTabbedPanel.onChange = function(){    var selectedTab = myPanel.grp.myTabbedPanel;    switch(selectedTab.selection.text){          case "Salidas":     //If Salidas was clicked...                                   myPanel.grp.myTabbedPanel.myTab1.ddPanel.selection = 0                             break;          case "Plecas":     //If Plecas was clicked...                     myPanel.grp.myTabbedPanel.myTab1.ddPanel.selection = 0                                 break;          //and so on for the other tabs you have.          default:          break;    }
}