Allow blank entry for drop down list fields

[#1]

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.  

[#2]

@RobertDo2 
at least for custom drop down fields you can do that, after opening dropdown just hit backspace key