The 'openstack overcloud update' command sought a list of events for each resource. When listing events for a resource, the Heat API returned a HTTP 404 error (Not Found) for resources with no events. The resource was considered as non-existent (due to the 404 error) and the client would fail. This occurred in situations where a previous update would end after adding a resource to the stack but before any events occur, such as a resource waiting at a breakpoint at the time the update ended. This fix adds error handling to the client, which resolves issues with the 404 error.