Add NULL check for multicast object.
Add NULL check for multicast object.

Change-Id: I2e4c5f741a4c8c366e909a69a46fd822c0cca95a
closes-bug: 1456954

numansiddique/contrail-controller,tcpcloud/contrail-controller,reiaaoyama/contrail-controller,sajuptpm/contrail-controller,rombie/contrail-controller,numansiddique/contrail-controller,codilime/contrail-controller,sajuptpm/contrail-controller,codilime/contrail-controller,hthompson6/contrail-controller,eonpatapon/contrail-controller,tcpcloud/contrail-controller,facetothefate/contrail-controller,rombie/contrail-controller,sajuptpm/contrail-controller,hthompson6/contrail-controller,eonpatapon/contrail-controller,vmahuli/contrail-controller,vpramo/contrail-controller,nischalsheth/contrail-controller,DreamLab/contrail-controller,reiaaoyama/contrail-controller,vmahuli/contrail-controller,rombie/contrail-controller,nischalsheth/contrail-controller,hthompson6/contrail-controller,sajuptpm/contrail-controller,sajuptpm/contrail-controller,reiaaoyama/contrail-controller,nischalsheth/contrail-controller,facetothefate/contrail-controller,codilime/contrail-controller,vmahuli/contrail-controller,DreamLab/contrail-controller,codilime/contrail-controller,eonpatapon/contrail-controller,tcpcloud/contrail-controller,numansiddique/contrail-controller,vpramo/contrail-controller,vmahuli/contrail-controller,nischalsheth/contrail-controller,tcpcloud/contrail-controller,codilime/contrail-controller,vmahuli/contrail-controller,eonpatapon/contrail-controller,reiaaoyama/contrail-controller,DreamLab/contrail-controller,vpramo/contrail-controller,nischalsheth/contrail-controller,facetothefate/contrail-controller,hthompson6/contrail-controller,sajuptpm/contrail-controller,eonpatapon/contrail-controller,facetothefate/contrail-controller,rombie/contrail-controller,rombie/contrail-controller,tcpcloud/contrail-controller,hthompson6/contrail-controller,rombie/contrail-controller,eonpatapon/contrail-controller,eonpatapon/contrail-controller,rombie/contrail-controller,nischalsheth/contrail-controller,codilime/contrail-controller,DreamLab/contrail-controller,nischalsheth/contrail-controller,reiaaoyama/contrail-controller,tcpcloud/contrail-controller,vpramo/contrail-controller,vpramo/contrail-controller,nischalsheth/contrail-controller,DreamLab/contrail-controller,facetothefate/contrail-controller,numansiddique/contrail-controller,numansiddique/contrail-controller