### Summary During code review, expanding some diffs (not all the diffs), we get a console error and rewiew feature is gone. ### Steps to reproduce 1. go to https://gitlab.com/gitlab-org/gitlab-runner/merge_requests/1218/diffs#7b841a9a815c326f2a4b4c1e4a026fc4a82b6e2f_321_322 1. expand the diff on the line above (322) 1. now you cannot add a new comment or complete an ongoing review (on EE) ### Relevant logs and/or screenshots <details> <summary>Collapsed screencast</summary> This screencast is on canary, but production has the same behavior.  </details> ``` TypeError: Cannot read property 'key' of undefined at Gn (vue.esm.js:5545) at vue.esm.js:5947 at E (vue.esm.js:6047) at vue.esm.js:5921 at E (vue.esm.js:6047) at vue.esm.js:5921 at E (vue.esm.js:6047) at a.__patch__ (vue.esm.js:6210) at a.e._update (vue.esm.js:2777) at a.i (vue.esm.js:2895) at It.get (vue.esm.js:3265) at It.run (vue.esm.js:3340) at Ot (vue.esm.js:3096) at Array.<anonymous> (vue.esm.js:1925) at Ke (vue.esm.js:1844) ``` ### Output of checks This bug happens on GitLab.com