WAB 2.7: widget not showing icon and is not added

[f-tonini]

I downloaded and unzipped you widget into the stemap widget folder. Then, when I go into WAB Dev Edition 2.7, and click to add the on-screen widget, it shows your widget with a missing icon (maybe broken link to icon.png?). Also, after selecting this widget (without icon), it shows a blank message with no text and clicking OK does not add the widget to its place. Please provide clarification.