"Invalid field access : visible" - Problems with Cocktail_Webview Sample (number 7)

[allop]

Hello!!
I'm new in Haxe and also in Cocktail, I'm trying to compile Sample number 7 from the repo. It works fine until I click on the button. Then the program closes and the following errors appear in the log:

Invalid field access : visible
Called from Main::onFlashClick line 124
Called from openfl._v2.events.Listener::dispatchEvent line 270
Called from openfl._v2.events.EventDispatcher::dispatchEvent line 100
Called from openfl._v2.display.DisplayObject::__dispatchEvent line 195
Called from openfl._v2.display.DisplayObject::__fireEvent line 271
Called from openfl._v2.display.Stage::__onMouse line 923
Called from openfl._v2.display.Stage::__doProcessStageEvent line 379

I really appreciate your time, as I need to fix this error for the job :/
Thanks!!
Anna