When using optional_end_date, the end date is still required

Problem/Motivation

When I use the https://www.drupal.org/project/optional_end_date module and configure my DateTimeRange field to have an optional end date, when I use any of the Smart Date widgets, I get a validation error that does not allow me to save the content (sorry I don't have the exact message, I'll replicate and provide more details about where the validation errors is coming from.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

None expected.

Data model changes

None expected.