How to show a custom title bar icon in NSWindow

gistfile1.m

// Force to show a titlebar icon
[window setRepresentedURL:[NSURL URLWithString:@"WindowTitle"]];
// Set our custom icon
[[window standardWindowButton:NSWindowDocumentIconButton] setImage:[NSImage imageNamed:@"imagename"]];

...

// Implement window delegate method to prevent to popup document (which do not exist) path menu when cmd+clicked
- (BOOL)window:(NSWindow *)window shouldPopUpDocumentPathMenu:(NSMenu *)menu
{
    return NO;
}