What is the XML rule for sys_user_has_role: Flag to avoid duplicate insertion in sys_user_has_role?

<rule>    <description>sys_user_has_role: Flag to avoid duplicate insertion in sys_user_has_role</description>    <comment xml:space="preserve">ServiceNow System allows duplicate rows/objects in relationship classes, such a sys_user_has_role. use this rule to set the flag to veto add operation if relationship already exists.</comment>    <conditions>        <and>            <if-operation mode="nocase" op="equal">add</if-operation>            <if-class-name mode="nocase" op="equal">sys_user_has_role</if-class-name>          </and>      </conditions>    <actions>        <do-set-xml-attr expression="." name="ignoreAddIfDuplicate">            <arg-string>                <token-text xml:space="preserve">true</token-text>              </arg-string>          </do-set-xml-attr>      </actions>  </rule>