Reset select-selector to undefined when cleared

[karwosts]

Proposed change

When clicking the clear button on a clearable select-selector, reset the value to undefined instead of "", as this better matches the initial state.

With the current implementation, in the template helper form if we pick a device class, and then clear it, the select field gets angry as "" is not one of the valid options. As the field is optional it should be clearable back to the initial state without a validation error.

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New feature (thank you!)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Example configuration

Additional information

• This PR fixes or closes issue: fixes #
• This PR is related to issue or discussion:
• Link to documentation pull request:

Checklist

• The code change is tested and works locally.
• There is no commented out code in this PR.
• Tests have been added to verify that the new code works.

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated for www.home-assistant.io

[frenck]

Thanks, @karwosts 👍

../Frenck