(node:15268) UnhandledPromiseRejectionWarning: TypeError: Cannot read property 'build' of undefined
at Object.character (*hide)
at Client. (*hide)
at processTicksAndRejections (internal/process/task_queues.js:93:5)
(node:15268) 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(). To terminate the node process on unhandled promise rejection, use the CLI flag --unhandled-rejections=strict (see https://nodejs.org/api/cli.html#cli_unhandled_rejections_mode). (rejection id: 2)
(node:15268) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

I used this tutorial

however, addField() works well!