Query strings and type safety
Query strings are usually strings, but - as some might not be aware of - can also be quite easily an array. So not checking on the type and blindly using it in stringish operations can currently cause undesired results.
So with the current implementation of how query strings (and named params) work, one should always assert the correct type first:
$result = 'string' . $this->request->getQuery('key'); // Dangerous without checking if set and a string