[Bug]: Undefined `footerClass` causes footer to be assigned `undefined` class

[chrstinalin]

Is there an existing issue for this?

• I have searched the existing issues

What happened?

When a Card's footer isn't a link or text and noStyle=false, a class of undefined is assigned to the footer.

Ex. Search card footer, paginator footers listed here

See: src/amo/components/Card/index.js#L55-L57 and src/amo/components/Card/index.js#L87

What did you expect to happen?

Either no additional class or a properly named class.

┆Issue is synchronized with this Jira Task