Improve error messages for `case`

From https://ask.clojure.org/index.php/9152/improve-error-messages-for-clojure-core-case

The error message generated when case encounters a non-matching clause uses str, resulting in nil being rendered as an empty string, and strings without quote marks.

For example:

And the potentially confusing

Would it be less ambiguous to use pr-str for the value resulting in nil and "1" respectively?

Note: a similar issue was raised for Clojurescript here:
https://ask.clojure.org/index.php/6575/improve-error-messages-using-instead-when-printing-objects