Add toString to fix bug in storybook

[matthew-gerstman]

Storybook seems to be passing integers to sanitize causing it to crash the application. I've tested that adding toString prevents it from breaking.

[matthew-gerstman]

FYI this happens whenever calling a function called add with a numeric literal passed to it inside of my applicattion source code

[zhyd1997]

Hey @matthew-gerstman

I faced the same issue and explained it in details here: storybookjs/storybook#18930 (comment)

[zhyd1997]

And I think white list (only accept string type) is better than black list (accept other types, eg. number and Object, and do some additional operations and then return string value) here.