I made this change just because jshint complains about using the type-coercing equality comparison (`==`) to check for any type of falsy value.  Using (`== null`) to check for `null` or `undefined` is not an uncommon practice.  But you can get into situations where you get false positives if you are not thinking about the possibility of an `undefined` value that will coerce to `null` in a comparison.  It is also possible for a programmer to make a change to such a check assuming that the intention is to catch values that are actually `null` when the original intention was to check for `undefined`.

In this case the store applies `JSON.stringify` to all stored values; so all values in the store should be truthy strings.  So a simpler truthiness check is appropriate.