writer.startElement("script", null);
        writer.writeText("ice.onUserInactivity(", null);
        writer.writeText(getInterval(), null);
        writer.writeText(", function() { document.getElementById('", null);
        writer.writeText(containerID, null);
        writer.writeText("').style.visibility = 'visible'; }", null);
        writer.writeText(", function() { document.getElementById('", null);
        writer.writeText(containerID, null);
        writer.writeText("').style.visibility = 'hidden'; });", null);
        writer.endElement("script");

should be modified so that null check is done before applying style.
In showcase app, if you select icecore:idleMonitor and then go to another example page, this component is still active and trying to change the style. Ideally, this is something visible on template throughout the entire application, but can foresee some instances (currently exhibited in showcase even if this was in the header for example so always visible, would still not be available in mobile showcase...)
So null check should be done.