Having the same issue on WP 5.0.2.
I have sites on the same server using 4.9.9 that are fine.
Uncaught TypeError: Cannot read property ‘length’ of undefined
at addMissingConvertersAndOptions (converters.js?ver=0.8.0-dev7:2)
at HTMLDocument.<anonymous> (converters.js?ver=0.8.0-dev7:26)
whitelist.js?ver=0.7.0-dev15:1 Uncaught TypeError: Cannot set property ‘value’ of null
at updateWhitelistInputValue (whitelist.js?ver=0.7.0-dev15:1)
at HTMLDocument.<anonymous> (whitelist.js?ver=0.7.0-dev15:22)
page.js?ver=0.7.0-dev5:1 Uncaught TypeError: Cannot read property ‘value’ of null
at updateCacheControlCustomVisibility (page.js?ver=0.7.0-dev5:1)
at HTMLDocument.<anonymous> (page.js?ver=0.7.0-dev5:6)
