Double equals with `null` is the one use case of double equals I use frequently because:

    null == null // true
    null == undefined // true

Rather than checking for both `null` and `undefined`, casting to null with `==` checks for both in a single statement.

This is noted in [jQuery's style guide](http://contribute.jquery.org/style-guide/js/#equality) as the one acceptable use of double equals as well.