Where exactly did you change JAVA_OPTS? If you changed a Windows or Linux environment variable, it is being overwritten when Wildfly starts. Assuming that you are in standalone mode, you'll need to modify the $WILDFLY_HOME/bin/standalone.conf (or standalone.conf.bat).
Modifying the sun\jdk module wouldn't work because that package isn't part of the JDK, but the JRE.
i am on a Windows box. i changed the standalone.con.bat.
the same settings with wildfly 9 work. but not with wildfly 13
ok i used the jdk....
when i change to the jre the ClassNotFoundException is gone.
But then i got an NullPointerExcetpion because
is returning null.
any idea how to solve this?