Update how graph results are fetched when they are optional.
Update how graph results are fetched when they are optional.

pombredanne/taskflow-1,varunarya10/taskflow,openstack/taskflow,jessicalucci/TaskManagement,jimbobhickville/taskflow,varunarya10/taskflow,junneyang/taskflow,pombredanne/taskflow-1,citrix-openstack-build/taskflow,junneyang/taskflow,jessicalucci/TaskManagement,jimbobhickville/taskflow,citrix-openstack-build/taskflow,openstack/taskflow