I'm submitting a ...

• bug report
• feature request
• other

Current behavior:

Log trace in the console :
TypeError: classString.split is not a function
at split (angular.js:27114)
at updateClasses (angular.js:27043)
at ngClassWatchAction (angular.js:27085)
at Scope.$digest (angular.js:18585)
at Scope.$apply (angular.js:18945)
at done (angular.js:12799)
at completeRequest (angular.js:13056)
at XMLHttpRequest.requestLoaded (angular.js:12961)
(anonymous) @ angular.js:15018
(anonymous) @ angular.js:11302
$digest @ angular.js:18603
$apply @ angular.js:18945
done @ angular.js:12799
completeRequest @ angular.js:13056
requestLoaded @ angular.js:12961
load (async)
(anonymous) @ angular.js:12944
sendReq @ angular.js:12744
serverRequest @ angular.js:12485
processQueue @ angular.js:17396
(anonymous) @ angular.js:17444
$digest @ angular.js:18557
$apply @ angular.js:18945
(anonymous) @ angular.js:28106
dispatch @ jquery-3.3.1.min.js:2
y.handle @ jquery-3.3.1.min.js:2

Expected / new behavior:

No such log trace.

Minimal reproduction of the problem with instructions:

I have no idea about what is generating the log trace. Maybe it's a misuse of the framework from me, but if so I don't know where my error is.

AngularJS version: 1.7.2

Browser: [all | Chrome XX | Firefox XX | Edge XX | IE XX | Safari XX | Mobile Chrome XX | Android X.X Web Browser | iOS XX Safari | iOS XX UIWebView | iOS XX WKWebView ]

I only tested with Chrome.

Anything else: