Using Hovercards on Wikidata, hovering over any item link says "Looks like there isn't a preview for this page". If I open the Console, I see the following error:
Exception in module-execute in module ext.gadget.PopupsFix: /w/load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=vector&version=0dwr6rr:176 TypeError: Cannot read property 'match' of null TypeError: Cannot read property 'match' of null at eval (eval at <anonymous> (/w/load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=vector&version=0dwr6rr:1), <anonymous>:1013:1430) at eval (eval at <anonymous> (/w/load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=vector&version=0dwr6rr:1), <anonymous>:1017:666) at Object.<anonymous> (/w/load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=vector&version=0dwr6rr:161) at fire (/w/load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=vector&version=0dwr6rr:45) at Object.add [as done] (/w/load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=vector&version=0dwr6rr:45) at Object.always (/w/load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=vector&version=0dwr6rr:46) at runScript (/w/load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=vector&version=0dwr6rr:161) at checkCssHandles (/w/load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=vector&version=0dwr6rr:161) at execute (/w/load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=vector&version=0dwr6rr:162) at Object.implement (/w/load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=vector&version=0dwr6rr:168)