JS error in Tag Manager preview mode #277
Description
In preview mode I get this error in renderPreviewFrame() from the tag manager preview.js:
Uncaught TypeError: document.body is null
renderPreviewFrame https://piwik.ub.uni-duesseldorf.de/piwik/js/container_B4dIhmVH_preview.js:34
Matomo Version is 3.14.1, Browser is Firefox 80.0.1 on OSX. The MTM-Code is added at the top of the <head> tag.
If I edit the preview.js and add a timeout that renderPreviewFrame() is delayed for a second, all is fine. Looks like that the browser needs to long to barse the body so that it is not yet initialized in the DOM when renderPreviewFrame() is called.