Allow blank entry for drop down list fields

Description - Allow blank entry for drop down list fields.

Why is this feature important to you - Currently, when you select a value and save, you are not able to change it back to blank.  The only way around this is to delete the task and create a new one.  

How would you like the feature to work - Allow list values to contain a blank or space value.

Current Behaviour - List values do not allow for blank or space values.