@apermo, please bear in mind this syntax is only valid since PHP 5.5. WordPress is pretty conservative with back-compat, so if you produce a plugin that may be installed on older version of PHP, please consider using an additional variable like @bhongy did.
the_content() also applies the the_content filter to the result of get_the_content(), so the method above might not actually work :/
Is there a use-case where this should be a problem for an empty check? Just wondering if I still use the_content() for displaying the content and empty check using get_the_content(), shouldn't be an issue right.