In Parameter command_script in the ssh-job no substitution takes place

When using $SCHEDULER_PARAM_NAME this will not be substituted but is vanishing.
When using \$SCHEDULER_PARAM_NAME this will not be substituted but is vanishing.
. parameter [command_script]: ls $SCHEDULER_PARAM_DIR

<?xml version="1.0" encoding="ISO-8859-1"?>

<job title="Launch remote commands or executable files by SSH"
name="SSHTest">
<settings>
<log_level><![CDATA[debug9]]></log_level>
</settings>
<description>
<include file="jobs/JobSchedulerSSHJob.xml"/>
</description>
<params>
<param name="host"
value="wilma"/>

<param name="port"
value="22"/>

<param name="user"
value="test"/>

<param name="command_delimiter"
value="%%"/>

<param name="password"
value="12345"/>

<param name="dir"
value="/home/test/scheduler.ur"/>

<param name="auth_method"
value="password"/>

<param name="command_script"
value="ls \$SCHEDULER_PARAM_DIR"/>
</params>
<script language="java"
java_class="sos.scheduler.job.JobSchedulerSSHJob"
java_class_path=""/>
<run_time/>
</job>