fix task.estimate_date nil exception
fix task.estimate_date nil exception

ari/jobsworth,digitalnatives/jobsworth,xuewenfei/jobsworth,digitalnatives/jobsworth,xuewenfei/jobsworth,digitalnatives/jobsworth,xuewenfei/jobsworth,digitalnatives/jobsworth,rafaspinola/jobsworth,rafaspinola/jobsworth,webstream-io/jobsworth,rafaspinola/jobsworth,webstream-io/jobsworth,xuewenfei/jobsworth,webstream-io/jobsworth,ari/jobsworth,ari/jobsworth,ari/jobsworth,webstream-io/jobsworth,digitalnatives/jobsworth,rafaspinola/jobsworth