Cannot read property 'toString' of undefined

[avoidwork]

Jun  9 00:35:45 blacky yc[1107]: (node:1107) UnhandledPromiseRejectionWarning: TypeError: Cannot read property 'toString' of undefined
Jun  9 00:35:45 blacky yc[1107]:     at /opt/yc/node_modules/tenso/lib/utility.js:513:26
Jun  9 00:35:45 blacky yc[1107]:     at each (/opt/yc/node_modules/tenso/lib/shared.js:8:3)
Jun  9 00:35:45 blacky yc[1107]:     at marshal (/opt/yc/node_modules/tenso/lib/utility.js:507:4)
Jun  9 00:35:45 blacky yc[1107]:     at /opt/yc/node_modules/tenso/lib/utility.js:598:7
Jun  9 00:35:45 blacky yc[1107]:     at each (/opt/yc/node_modules/tenso/lib/shared.js:8:3)
Jun  9 00:35:45 blacky yc[1107]:     at hypermedia (/opt/yc/node_modules/tenso/lib/utility.js:596:5)
Jun  9 00:35:45 blacky yc[1107]:     at Tenso.send (/opt/yc/node_modules/tenso/lib/tenso.js:492:64)
Jun  9 00:35:45 blacky yc[1107]:     at ServerResponse.res.send (/opt/yc/node_modules/woodland/lib/woodland.js:172:30)
Jun  9 00:35:45 blacky yc[1107]:     at /api/search (/opt/yc/lib/routes.js:56:11)
Jun  9 00:35:45 blacky yc[1107]:     at processTicksAndRejections (internal/process/task_queues.js:89:5)
Jun  9 00:35:45 blacky yc[1107]: (node:1107) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 6)