René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"`getTree` fails on result of `commit.parent(0)`","articleBody":"## System information\r\n  - node version: v8.12.0\r\n  - yarn version: 1.5.1\r\n  - OS/version/architecture: darwin/18.2.0/x64\r\n  - Applicable nodegit version: nodegit@0.25.0-alpha.9 (also repros in 0.24.1 and 0.23.0)\r\n\r\n## Repro\r\n\r\nHere's a repro that runs against the `nodegit` git repo:\r\n\r\n```js\r\nconst nodegit = require('nodegit');\r\n\r\nnodegit.Repository.open('../nodegit').then(repo =\u003e {\r\n  return repo.getCommit('977251b4aae52eef75cf4f188b4d5a63ba98fa7b')\r\n}).then(commit =\u003e {\r\n  return commit.parent(0);\r\n}).then(parentCommit =\u003e {\r\n  return parentCommit.getTree();\r\n}).then(parentTree =\u003e {\r\n  console.log('parentTree: ' + parentTree);\r\n}).then(null, err =\u003e {\r\n  console.log('Error encountered\\n');\r\n  console.log(err);\r\n});\r\n```\r\n\r\n**Expected output:** `parentTree: [object Tree]`\r\n\r\n**Actual output:**\r\n\r\n```\r\nError encountered\r\n\r\nTypeError: Cannot read property 'getTree' of undefined\r\n    at Commit.getTree (node_modules/nodegit/dist/commit.js:302:20)\r\n    at nodegit.Repository.open.then.then.then.parentCommit (main.js:11:23)\r\n    at tryCallOne (node_modules/nodegit-promise/lib/core.js:37:12)\r\n    at node_modules/nodegit-promise/lib/core.js:103:15\r\n    at flush (node_modules/asap/raw.js:50:29)\r\n    at _combinedTickCallback (internal/process/next_tick.js:132:7)\r\n    at process._tickCallback (internal/process/next_tick.js:181:9)\r\n```\r\n\r\nIt looks like [this line](https://github.com/nodegit/nodegit/blob/7851e931a54ca487fb6556ab8713c94ac1719efb/lib/commit.js#L352) throws an exception because `this.repo` is `undefined`.","author":{"url":"https://github.com/rigdern","@type":"Person","name":"rigdern"},"datePublished":"2019-03-31T16:57:42.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":1},"url":"https://github.com/1653/nodegit/issues/1653"}