URL to be opened is not displayed in the link opening UI

To reproduce: Make sure web links are enabled, then run the following command and click on "Clicky!" in the chat:

/tellraw @a {text:"",extra:[{text:Clicky!,clickEvent:{action:open_url,value:"http://google.com/"}}]}

The resulting popup will not display the URL you would be taken to. See attached screenshot.

Relates to MC-30864.