how to put the '(All)' value in filter by using req_option

[irisx0719]

Describe the bug
I have several filter put in report, the original view is setting filter as value 'a' and when I pulled the data through script, I want to include them all, I used req_option and set the value as '(All)', but there is no changes

To Reproduce.

po_req_option.vf('Risk Category', '(All)')

Results
no thing different compare to the original view data

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