User Picker Custom Fields should have drop-down-box for "Current User" etc. when searching for issues

We have a custom user picker field and now I need to create a global filter which filters all issues where the value of this field is set to the current user. But currently you can only enter a fixed value, i. e. one specific user-name for the search. This is inadequate for Global Filters.

I suggest to have a drop-down box just like e. g. for the assignee, i. e. a list with values:

• Any User
• Empty/Not Set
• Current User
• Specify User
• Specify Group