Fixed failure when review history is empty
Fixed failure when review history is empty

Closed bug 1208806

Change-Id: Id256d3c0e5814da4add6ccf318bcf30f82d791d3

stackforge/stackalytics,openstack/stackalytics,zxiiro/spectrometer,nihilifer/stackalytics,dave-tucker/spectrometer,mgkwill/spectrometer,dliu2015/stackalytics_zanata,mgkwill/spectrometer,mgkwill/spectrometer,mhharsh/stackalytics,Mirantis/stackalytics,AlexanderYAPPO/stackalytics,mhharsh/stackalytics,Solinea/stackalytics,zxiiro/spectrometer,0xf2/stackalytics,zxiiro/spectrometer,Mirantis/stackalytics,alexpilotti/stackalytics-1,dave-tucker/spectrometer,Code-Fly/stackalytics,mgkwill/spectrometer,stackforge/stackalytics,Mirantis/stackalytics,joshuamckenty/stackalytics,mohitsethi/stackalytics,AlexanderYAPPO/stackalytics,danielmellado/stackalytics,zxiiro/spectrometer,stackforge/stackalytics,Code-Fly/stackalytics,mhharsh/stackalytics,Solinea/stackalytics,dave-tucker/spectrometer,AlexanderYAPPO/stackalytics,zxiiro/spectrometer,nihilifer/stackalytics,0xf2/stackalytics,dave-tucker/spectrometer,alexpilotti/stackalytics-1,mohitsethi/stackalytics,danielmellado/stackalytics,dliu2015/stackalytics_zanata,openstack/stackalytics,Code-Fly/stackalytics,openstack/stackalytics,Solinea/stackalytics,dliu2015/stackalytics_zanata,openstack/stackalytics,dave-tucker/spectrometer,kevinbenton/stackalytics,joshuamckenty/stackalytics,0xf2/stackalytics,kevinbenton/stackalytics,mgkwill/spectrometer,nihilifer/stackalytics,0xf2/stackalytics,mohitsethi/stackalytics,danielmellado/stackalytics