Cannot purge the home page or '/'

Problem/Motivation

We are trying to purge only the home page so '/' and when we try that with the path option we get the error 'Exception while trying to invalidate the items: Path invalidations cannot start with slashes.'

Note that in CloudFront we can specific just '/' and that invalidates the home page correctly. Is there a way to do that with the module?

Entering "/" in the Purge Invalidation Form fails because purge core
rejects path expressions starting with a slash.

Steps to reproduce

Setup the module as per the documentation.

1. Navigate to Configuration -> Development -> Performance
2. Click 'Purge Invalidation Form'
3. Select 'Type' of 'Path'
4. Enter just / in the 'Item' textarea
5. Click 'Purge'
6. Confirm the error

Proposed resolution

Treat an empty
expression and the "" keyword as equivalent, both resolving to
the CloudFront invalidation path "/".

Remaining tasks

1. Verify the bug and proposed solution.
2. Add solution.
3. Release new beta version

User interface changes

Potentially adding a new drop-down.