Power BI Data Function Button - Allow submission when input slicer is blank

Currently data function button submission in Power BI requires all parameters not blank. Otherwise, the button is disabled. A typical scenario is what we want user to rate and provide comments (optional) through Power BI. The rating comes from a measure and the comments field is from an input slicer. As the comments field is optional, user doesn't have to always provide comments when submitting the rating. However, due to that data function requires to be not blank, the button won't be enabled until user provides the comments.

Fabric user data function now supports setting default value to parameter, but this doesn't work in the button action configuration in Power BI.