## Description
See issue #8653
## Specific Changes proposed
When in `middleware.js` the function `clearCacheForPlayer` runs, before
setting a value to null in middlware caches, it checks if the key exists
in the first place.
## Requirements Checklist
- [x] Feature implemented / Bug fixed
- [x] If necessary, more likely in a feature request than a bug fix
- [x] Change has been verified in an actual browser (Chrome, Firefox,
IE)
- [ ] Unit Tests updated or fixed
- [ ] Docs/guides updated
- [x] Example created ([starter template on
JSBin](https://codepen.io/gkatsev/pen/GwZegv?editors=1000#0))
- [ ] Reviewed by Two Core Contributors
---------
Co-authored-by: Giuseppe Piscopo <g.piscopo@braincrumbz.com>
Co-authored-by: mister-ben <git@misterben.me>
