saveFile() tries to call a non-function callback
grapheditorxblock/src/js/grapheditorxblock.js we have a
saveFile() function that is supposed to be called with a callback functions as a parameter. Apparently the check we do on that does not suffice:
if (typeof callback != "undefined") callback();
TypeError: callback is not a function
Not sure if this is relevant: I consistently get that error (hidden in the console of course) when saving in the studio view in my local development environment while testing the graphxblock stand-alone. I have not yet tested other situations. Even with that error message, saving seems to work fine, so this is a low-priority issue.