How can we set Arrayset's Single select picklist attribute value as blank from recommendation rule?

Summary:

Customer selected value in arrayset's dynamic SSPL attribute and after that there was requirement to set that value as blank when particular boolean is checked. I wrote recommendation rule and tried to update that value as blank but it is not getting updated to blank but when I'm trying to set it to some other value which is present in data table then it is getting updated.

SSPL Attribute's set type is set at attribute level as well as on recommendation rule.