NullPointer exception when slave tries to scale down

<ha-policy>
   <shared-store>
      <slave>
         <failover-on-shutdown>true</failover-on-shutdown>
         <restart-backup>true</restart-backup>
         <scale-down>
           <connectors>
             <connector-ref>master1-connector</connector-ref>
           </connectors>
         </scale-down>
      </slave>
   </shared-store>
</ha-policy>