Empty keys are registry entries with null data. One of the common causes of these empty keys is the hard drive space left behind when you uninstall applications and softwares from your computer. These empty keys would increase the size of the registry and hence degrade the performance of your computer. In order to enhance the computer's performance you must clean these empty keys periodically to avoid piling up of these empty keys. It is safe to remove these keys as these keys don’t have any content in them.