Trying to get property of non-object in node_help() (line 135 of core/modules/node/node.module)

PHP error notice displayed when tried to edit a language version of node.

Steps to reproduce this issue:

1. Install fresh D8;
2. Enable Content Translation module;
3. Edit article content type;
4. Enable translation under language settings;
5. Edit article content type, click manage fields;
6. Edit body;
7. Enable translation for body field;
8. In configuration, add languages;
9. Create test article;
10. Click translations tab;
11. Add other language versions for the node;
12. Click 'edit' to edit existing version of translations (Not the original copy);

The error notice will display as screenshot.

Line 135 in node module is trying to get node->type. This error displayed because the node didn't get loaded, as arg[1] is 'node' instead of nid.