getting "Invalid rewrite directive" for rewritemap rule

I am trying to add a rewritemap directive under static context and getting "invalid rewrite directive" error, wondering whether rewritemap is supported by openlitespeed. I am using version 1.7.14. i am using a "static context" with following rewrite rules.

RewriteEngine On
RewriteMap hook "prg:/home/test/sessionvalidater"
RewriteCond %{REQUEST_URI} /sessionvalidate\?(.*)
RewriteRule (.*) ${hook:$1}