XWQL doesn't support LOWER, UPPER, CONCAT or any other function in LIKE expressions

#set ($authors = $services.query.xwql("SELECT doc.fullName FROM Document doc, doc.object(XWiki.XWikiUsers) obj where obj.first_name like lower('%DMIN%')  ").execute())
#foreach($author in $authors)
 #set($docAuthor = $xwiki.getDocument("$author"))
  <rs id="" info="$author">$!docAuthor.first_name $!docAuthor.last_name</rs>
#end

Caused by: org.xwiki.query.jpql.parser.ParserException: [1,99] expecting: string literal, input parameter
	at org.xwiki.query.jpql.parser.Parser.parse(Parser.java:1385)
	at org.xwiki.query.jpql.internal.JPQLParser.parse(JPQLParser.java:46)
	at org.xwiki.query.xwql.internal.hql.XWQLtoHQLTranslator.translate(XWQLtoHQLTranslator.java:55)
	at org.xwiki.query.xwql.internal.XWQLQueryExecutor.execute(XWQLQueryExecutor.java:90)