Feature Request

It would be useful if there was a way to distinguish between passing a string flag a blank string (command -f "") and the absence of the flag (command).

Currently both will return "" from c.String("f")

Our use case:

We have a command to update a resource via an API. Fields that can be updated are represented by different CLI flags. One of the fields on the resource is a string that can be blank. We would like users to be able to set the field to the blank string.

#Setting the field to non-blank string
command -f "string"

#Setting the field to blank string
command -f ""

To do this currently we have to have another flag to reset the field.

command --clear-field

This is annoying because it means we have two flags for a single field and have to handle cases where both flags are passed.

Thanks!