Bot crashes if it cannot find a user/username

[Al3366]

Any commands that requires a users name, like !love @user, crash the bot if it cannot get the username.
When you only type the name of the user without the @ symbol: http://i.imgur.com/UJPkxG8.png
When you use the @ symbol with a username: http://i.imgur.com/YvOU8o7.png