JSDoc for getCachedToken indicates only a string is returned

[justrhysism]

The return type should be string|null - typings will need to be updated also.

react-adal/src/adal.js

Line 410 in d859675

* @returns {string} token if if it exists and not expired, otherwise null.

Line where null is returned:

react-adal/src/adal.js

Line 428 in d859675

return null;