# Create/Update .md files -- Unable to open: Assertion Failed: Argument is ‘undefined’ or ‘null’ **URL:** \ **Category:** Bug Reports\ **Created:** [October 30, 2025, 7:54pm UTC](https://forum.cursor.com/t/create-update-md-files-unable-to-open-assertion-failed-argument-is-undefined-or-null/140018 "2025-10-30T19:54:50Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![dragidude](https://avatars.discourse-cdn.com/v4/letter/d/e480ec/32.png) [@dragidude](https://forum.cursor.com/u/dragidude)\ **Post date:** [October 30, 2025, 7:54pm UTC](https://forum.cursor.com/t/create-update-md-files-unable-to-open-assertion-failed-argument-is-undefined-or-null/140018/1 "2025-10-30T19:54:50Z")
### Where does the bug appear (feature/product)? Cursor IDE ### Describe the Bug Cursor 2.0 often creates .md which cannot be opened in the IDE. Unable to open ‘documentation.md’ Assertion Failed: Argument is ‘undefined’ or ‘null’ This disrupts my workflow quite a bit because I constantly make and update .md files. They are the “memory”. I’m on Windows and don’t have any special add-ons or MCPs or anything. I find if I open the doc before the agent updates, it’s less like to have an issue. The agents I use are Sonnet 4.5 Thinking and Composer 1.0. ### Steps to Reproduce Ask the agent to create a .md file for documentation or planning. ### Expected Behavior The .md file should be openable in the IDE by clicking on it from the file explorer. This is very basic functionality. ### Screenshots / Screen Recordings ![cursor_error.jpg](https://us1.discourse-cdn.com/cursor1/original/3X/d/e/dee929bd5bc54f9c38f8148453a2ac47a52d4626.jpeg) ### Operating System Windows 10/11 ### Current Cursor Version (Menu → About Cursor → Copy) Version: 2.0.38 (system setup) VSCode Version: 1.99.3 Commit: 3fa438a81d579067162dd8767025b788454e6f90 Date: 2025-10-29T20:45:40.883Z Electron: 34.5.8 Chromium: 132.0.6834.210 Node.js: 20.19.1 V8: 13.2.152.41-electron.0 OS: Windows\_NT x64 10.0.17763 ### For AI issues: which model did you use? Sonnet 4.5 and Composer. ### Does this stop you from using Cursor Sometimes - I can sometimes use Cursor ---
**Author:** ![sanjeed5](https://sea3.discourse-cdn.com/cursor1/user_avatar/forum.cursor.com/sanjeed5/32/9610_2.png) [@sanjeed5](https://forum.cursor.com/u/sanjeed5)\ **Post date:** [October 31, 2025, 2:53pm UTC](https://forum.cursor.com/t/create-update-md-files-unable-to-open-assertion-failed-argument-is-undefined-or-null/140018/2 "2025-10-31T14:53:43Z")
Thanks for the detailed bug report! To help us debug this, could you please share: 1. Open Help \> Toggle Developer Tools and check the Console tab when the error appears - share any error messages you see there 2. Can you open the problematic .md file using File \> Open or in an external text editor (like Notepad)? 3. Does this happen with all .md filenames or specific patterns (e.g., files with spaces, special characters)? 4. What’s the file path where these .md files are being created? Also, please try disabling extensions - they can cause unexpected file opening issues: - Run `cursor --disable-extensions` from command line - If .md files open correctly, re-enable extensions one by one to find the culprit or use Extension bisect ---
**Author:** ![dragidude](https://avatars.discourse-cdn.com/v4/letter/d/e480ec/32.png) [@dragidude](https://forum.cursor.com/u/dragidude)\ **Post date:** [October 31, 2025, 8:29pm UTC](https://forum.cursor.com/t/create-update-md-files-unable-to-open-assertion-failed-argument-is-undefined-or-null/140018/3 "2025-10-31T20:29:45Z")
Thanks for the detailed bug report! To help us debug this, could you please share: 1. Open Help \> Toggle Developer Tools and check the Console tab when the error appears - share any error messages you see there 2. Can you open the problematic .md file using File \> Open or in an external text editor (like Notepad)? 3. Does this happen with all .md filenames or specific patterns (e.g., files with spaces, special characters)? 4. What’s the file path where these .md files are being created? Also, please try disabling extensions - they can cause unexpected file opening issues: - Run `cursor --disable-extensions` from command line - If .md files open correctly, re-enable extensions one by one to find the culprit or use Extension bisect ---
**Author:** ![dragidude](https://avatars.discourse-cdn.com/v4/letter/d/e480ec/32.png) [@dragidude](https://forum.cursor.com/u/dragidude)\ **Post date:** [October 31, 2025, 8:55pm UTC](https://forum.cursor.com/t/create-update-md-files-unable-to-open-assertion-failed-argument-is-undefined-or-null/140018/4 "2025-10-31T20:55:17Z")
Thanks Sanjeed, I love Cursor 2.0, but this “bug” is causing me pain because I make a .md for every page of my website. Below is an analysis (written in cursor, of course!) Thank you for the follow-up. Here are the details and our findings.## Console errorsFrom Developer Tools \> Console: ERR Unable to retrieve document from URI ‘file:///d%3A/inetpub/wwwroot/askARTreact/docs/admin/reports/ad-reporting.md’: Error: Unable to retrieve document from URI ‘file:///d%3A/inetpub/wwwroot/askARTreact/docs/admin/reports/ad-reporting.md’ Lyu: Assertion Failed: Argument is `undefined` or `null`. The error occurs when trying to open programmatically created markdown files immediately after creation.## External editorsYes, files open correctly in:- Notepad++ - PowerShell (Get-Content) - VS Code (if installed) - Windows Notepad Files exist, have correct content and encoding, and are readable by other tools. The issue is Cursor-specific.## Filename patternsAffects all .md files created programmatically:- Files with spaces: MD file creation issue.md — fails if created programmatically - Files with hyphens: ad-reporting.md — fails if created programmatically - Simple names: test.md — fails if created programmatically - No special characters required; any programmatically created file fails Files manually created in Cursor (File \> New) work immediately.## File pathsIssue occurs at:- D:\inetpub\wwwroot\askARTreact\docs\admin\reports\ad-reporting.md - D:\inetpub\wwwroot\askARTreact\docs\0 Common\Windows-File-Creation-Issue.md - Any path in the workspace where files are created programmatically ## Extension testingTested with cursor --disable-extensions: issue persists. This appears to be a core Cursor IDE issue, not extension-related.## Root cause analysisAfter testing:1. Problem: Files created programmatically (via AI write tool, PowerShell, etc.) cannot be opened in Cursor immediately. They show: - “Unable to retrieve document from URI” - “Assertion Failed: Argument is ‘undefined’ or ‘null’” 1. Workaround: Restarting Cursor IDE allows the files to open. This suggests a file system watcher cache issue. 2. Solution found: Files manually created in Cursor (File \> New, then save) open immediately and remain accessible. Populating those files programmatically works fine. 3. Root cause hypothesis: Cursor’s Electron-based file system watcher on Windows is not registering programmatically created files. The watcher relies on OS-level file system events that may not fire for files created by external tools. Restarting forces a full file system rescan, which registers the files. 4. Regression: This started after upgrading to Cursor 2.0. The previous version did not have this issue. ## Evidence- Programmatically created files fail to open immediately - Same files open after Cursor restart - Same files open in external editors immediately - Manually created files work immediately - Issue affects all programmatically created .md files, regardless of filename pattern - Issue persists with all extensions disabled - Not related to file encoding, content, or permissions ## RecommendationThis appears to be a regression in Cursor 2.0’s file system watcher. Please investigate:1. The file system watcher implementation on Windows 1. How programmatically created files are registered 2. Why manually created files are immediately accessible while programmatically created files are not The workaround (manual file creation) is functional but not ideal for workflows that rely on programmatic file creation.Please let me know if you need additional details or test cases. > ![](https://sea3.discourse-cdn.com/cursor1/user_avatar/forum.cursor.com/sanjeed5/45/9610_2.png "sanjeed5") | [sanjeed5](https://forum.cursor.com/u/sanjeed5) Community Developer > October 31 | > > - | - | Thanks for the detailed bug report! To help us debug this, could you please share: 1. Open Help \> Toggle Developer Tools and check the Console tab when the error appears - share any error messages you see there 2. Can you open the problematic .md file using File \> Open or in an external text editor (like Notepad)? 3. Does this happen with all .md filenames or specific patterns (e.g., files with spaces, special characters)? 4. What’s the file path where these .md files are being created? Also, please try disabling extensions - they can cause unexpected file opening issues: - Run `cursor --disable-extensions` from command line - If .md files open correctly, re-enable extensions one by one to find the culprit or use Extension bisect ---
**Author:** ![KurnosovNikita](https://avatars.discourse-cdn.com/v4/letter/k/cab0a1/32.png) [@KurnosovNikita](https://forum.cursor.com/u/KurnosovNikita)\ **Post date:** [November 2, 2025, 6:07pm UTC](https://forum.cursor.com/t/create-update-md-files-unable-to-open-assertion-failed-argument-is-undefined-or-null/140018/5 "2025-11-02T18:07:09Z")
Same here — I use Cursor to generate and update many Markdown files, and since the major update, I’ve been running into this issue every time after an agent update or when generating a Markdown file. As a workaround, I have to close the file, accept the changes blindly, and then reopen it. Cursor becomes practically unusable this way. Please fix it as soon as possible. ---
**Author:** ![sanjeed5](https://sea3.discourse-cdn.com/cursor1/user_avatar/forum.cursor.com/sanjeed5/32/9610_2.png) [@sanjeed5](https://forum.cursor.com/u/sanjeed5)\ **Post date:** [November 3, 2025, 2:25pm UTC](https://forum.cursor.com/t/create-update-md-files-unable-to-open-assertion-failed-argument-is-undefined-or-null/140018/7 "2025-11-03T14:25:34Z")
Thanks for the details, I’ve passed it on to the team. ---
**Author:** ![galenking](https://sea3.discourse-cdn.com/cursor1/user_avatar/forum.cursor.com/galenking/32/85912_2.png) [@galenking](https://forum.cursor.com/u/galenking)\ **Post date:** [November 4, 2025, 7:49pm UTC](https://forum.cursor.com/t/create-update-md-files-unable-to-open-assertion-failed-argument-is-undefined-or-null/140018/8 "2025-11-04T19:49:37Z")
I get this constantly, too! ---
**Author:** ![fox](https://avatars.discourse-cdn.com/v4/letter/f/c5a1d2/32.png) [@fox](https://forum.cursor.com/u/fox)\ **Post date:** [November 4, 2025, 8:17pm UTC](https://forum.cursor.com/t/create-update-md-files-unable-to-open-assertion-failed-argument-is-undefined-or-null/140018/9 "2025-11-04T20:17:50Z")
Also observing this with markdown files. Very frustrating. I think this might only affect markdown files created by the agent (?). ---
**Author:** ![banksjim](https://sea3.discourse-cdn.com/cursor1/user_avatar/forum.cursor.com/banksjim/32/86148_2.png) [@banksjim](https://forum.cursor.com/u/banksjim)\ **Post date:** [November 6, 2025, 3:47am UTC](https://forum.cursor.com/t/create-update-md-files-unable-to-open-assertion-failed-argument-is-undefined-or-null/140018/10 "2025-11-06T03:47:55Z")
### Where does the bug appear (feature/product)? Cursor IDE ### Describe the Bug **Title:** Markdown preview fails with “Assertion Failed” error after AI tool modifications * * * ### Description Markdown files that are created or modified using Cursor’s AI assistant tools (`write` and `search_replace`) become unrenderable in Cursor’s markdown preview pane, showing an “Assertion Failed: Argument is `undefined` or `null`” error. The files remain valid markdown and can be opened in the raw markdown editor. ### Symptoms - **Error Message** : “Assertion Failed: Argument is `undefined` or `null`” - **Location** : Markdown preview pane when attempting to open `.md` files - **Files Affected** : Multiple markdown documentation files in a git-tracked workspace - **Content** : Files are syntactically valid markdown but fail to render in preview ### Steps to Reproduce ### Steps to Reproduce 1. Open Cursor in a git-tracked workspace with markdown files 2. Use AI assistant to create a new markdown file with the `write` tool - Example: Create `docs/status/TEST-FILE.md` with markdown content 3. Attempt to open the file in Cursor’s markdown preview 4. **Result** : “Assertion Failed” error appears instead of rendered preview **OR** 1. Have an existing, working markdown file in the workspace 2. Use AI assistant’s `search_replace` tool to modify the file 3. Attempt to reopen the file in Cursor’s markdown preview 4. **Result** : File that previously worked now shows “Assertion Failed” error ### Expected Behavior ### Expected Behavior Markdown files created or modified by Cursor’s AI tools should render normally in the markdown preview pane, just like manually edited files. ### Actual Behavior Files become corrupted in a way that prevents Cursor’s markdown preview from rendering them, even though: - The markdown syntax is valid - The files can be opened in the raw markdown editor - The files can be read by other markdown tools - Git shows valid, readable content ### What We Tested (None of these fixed the issue) 1. ❌ Correcting markdown syntax errors (MD019, MD026, MD029) 2. ❌ Removing emojis and special characters 3. ❌ Removing extended file attributes (`xattr -c file.md`) 4. ❌ Recreating files from scratch using `write` tool 5. ❌ Creating files with OS `cp` command, then editing with `search_replace` (breaks after AI edit) 6. ❌ Restoring files from git history (`git show commit:path > file`) 7. ❌ Recreating files using terminal commands (cat, echo, heredocs) ### Screenshots / Screen Recordings ![mderror.png](https://us1.discourse-cdn.com/cursor1/original/3X/c/5/c532a809bbc0e3804871f77e075d11d4bdd35b31.png) ### Operating System MacOS ### Current Cursor Version (Menu → About Cursor → Copy) Version: 2.0.63 Commit: 505046dcfad2acda3d066e32b7cd8b6e2dc1fdc0 Date: 2025-11-05T18:56:58.213Z Browser: Mozilla/5.0 (Macintosh; Intel Mac OS X 10\_15\_7) AppleWebKit/537.36 (KHTML, like Gecko) Cursor/2.0.63 Chrome/138.0.7204.251 Electron/37.7.0 Safari/537.36 ### For AI issues: which model did you use? claude-4.5-sonnet ### Additional Information ### Workarounds That DO Work 1. ✅ **Temporary fix** : Open file → Click “Switch to Markdown Editor” → Close file → Reopen 2. ✅ **Temporary fix** : Clear Cursor cache ### Key Observations 1. **Files created by OS tools initially work** : Using `cp` to copy a working markdown file creates a working copy 2. **AI tool edits break files** : Using `search_replace` on the copied file makes it unrenderable 3. **Git restore doesn’t fix** : Even `git show` from clean history produces broken files 4. **Corruption is in Cursor’s metadata** : The actual file content is valid markdown, suggesting Cursor’s internal file tracking/caching is corrupted ### Environment - **Operating System** : macOS 24.6.0 (Sonoma) - **Cursor Version** : 2.0.63 - **Cursor Commit** : 505046dcfad2acda3d066e32b7cd8b6e2dc1fdc0 - **Cursor Date** : 2025-11-05T18:56:58.213Z - **Electron** : 37.7.0 - **Chrome** : 138.0.7204.251 - **Workspace** : Git-tracked repository - **File Type** : Standard markdown (.md) files - **Shell** : /bin/zsh ### Affected Files Multiple markdown documentation files in the `docs/` directory became unrenderable after AI tool modifications. Example file `docs/status/RESUME-HERE.md` can be provided if needed for debugging. ### Impact - **Severity** : Medium - Prevents normal usage of markdown preview feature - **Workaround Available** : Yes, but tedious (must manually fix each file) - **Frequency** : Consistent - happens every time AI tools modify markdown files - **User Impact** : Disrupts workflow, requires manual intervention to fix files ### Additional Notes This appears to be a bug in how Cursor’s AI tools (`write`, `search_replace`) interact with Cursor’s markdown preview metadata/caching system. The tools create or modify files in a way that Cursor’s preview can’t handle, even though the files are technically valid. **Hypothesis** : The AI tools may be bypassing or not properly updating some internal Cursor file tracking/indexing mechanism that the markdown preview relies on. ### Reproduction Reliability ✅ **Highly reproducible** - Happened consistently across multiple sessions and multiple files ### Does this stop you from using Cursor No - Cursor works, but with this issue ---
**Author:** ![master3395](https://sea3.discourse-cdn.com/cursor1/user_avatar/forum.cursor.com/master3395/32/46687_2.png) [@master3395](https://forum.cursor.com/u/master3395)\ **Post date:** [November 5, 2025, 7:20pm UTC](https://forum.cursor.com/t/create-update-md-files-unable-to-open-assertion-failed-argument-is-undefined-or-null/140018/11 "2025-11-05T19:20:43Z")
### Where does the bug appear (feature/product)? Cursor IDE ### Describe the Bug When i ask Cursor to make .md files, it doesn’t load most of them anymore. Even if they are created. ### Steps to Reproduce All i did was update cursor to latest version, and then it stopped working, when i made projects, and asked it to make summary using .md ### Expected Behavior It should load the .md ### Screenshots / Screen Recordings ![Skjermbilde 2025-11-05 201838.png](https://us1.discourse-cdn.com/cursor1/original/3X/1/2/121049a72fea7ab8689b684a80fd2c83c41e8538.png) ### Operating System Windows 10/11 ### Current Cursor Version (Menu → About Cursor → Copy) Version: 2.0.43 (user setup) VSCode Version: 1.99.3 Commit: 8e4da76ad196925accaa169efcae28c45454cce0 Date: 2025-10-30T18:49:27.589Z Electron: 34.5.8 Chromium: 132.0.6834.210 Node.js: 20.19.1 V8: 13.2.152.41-electron.0 OS: Windows\_NT x64 10.0.26200 ### For AI issues: which model did you use? Auto ### Does this stop you from using Cursor Sometimes - I can sometimes use Cursor ---
**Author:** ![altruistic](https://avatars.discourse-cdn.com/v4/letter/a/22d042/32.png) [@altruistic](https://forum.cursor.com/u/altruistic)\ **Post date:** [November 6, 2025, 2:57pm UTC](https://forum.cursor.com/t/create-update-md-files-unable-to-open-assertion-failed-argument-is-undefined-or-null/140018/12 "2025-11-06T14:57:27Z")
whole of our company has the same iussue ---
**Author:** ![Yan\_C](https://avatars.discourse-cdn.com/v4/letter/y/9e8a1a/32.png) [@Yan\_C](https://forum.cursor.com/u/Yan_C)\ **Post date:** [November 7, 2025, 4:48pm UTC](https://forum.cursor.com/t/create-update-md-files-unable-to-open-assertion-failed-argument-is-undefined-or-null/140018/13 "2025-11-07T16:48:51Z")
In my case, the issues comes from the “Office Viewer” extension, that bug only appeared since cursor 2.0. To temporarily solve the issue: Disable Office Viewer, reload extension, open file to confirm, then you can reactivate Office Viewer and reopen the file (if you really need that view) Hopefully that can help someone ---
**Author:** ![master3395](https://sea3.discourse-cdn.com/cursor1/user_avatar/forum.cursor.com/master3395/32/46687_2.png) [@master3395](https://forum.cursor.com/u/master3395)\ **Post date:** [November 7, 2025, 10:07pm UTC](https://forum.cursor.com/t/create-update-md-files-unable-to-open-assertion-failed-argument-is-undefined-or-null/140018/14 "2025-11-07T22:07:47Z")
I’ll try this next time i make a project with .md 🙂 ---
**Author:** ![abohassan19](https://sea3.discourse-cdn.com/cursor1/user_avatar/forum.cursor.com/abohassan19/32/81346_2.png) [@abohassan19](https://forum.cursor.com/u/abohassan19)\ **Post date:** [November 7, 2025, 11:11pm UTC](https://forum.cursor.com/t/create-update-md-files-unable-to-open-assertion-failed-argument-is-undefined-or-null/140018/15 "2025-11-07T23:11:44Z")
This worked for me, thank you! ---
**Author:** ![Kwickell](https://avatars.discourse-cdn.com/v4/letter/k/bc79bd/32.png) [@Kwickell](https://forum.cursor.com/u/Kwickell)\ **Post date:** [November 11, 2025, 10:09am UTC](https://forum.cursor.com/t/create-update-md-files-unable-to-open-assertion-failed-argument-is-undefined-or-null/140018/16 "2025-11-11T10:09:15Z")
Been an issue for me as well. All started after the 2.0 update. ```auto workbench.desktop.main.js:55 ERR Unable to retrieve document from URI 'file:///home/kwickell/code/Playpilot/n8n/memory-bank/activeContext.md': Error: Unable to retrieve document from URI 'file:///home/kwickell/code/Playpilot/n8n/memory-bank/activeContext.md' at uUt.getDocument (file:///usr/share/cursor/resources/app/out/vs/workbench/api/node/extensionHostProcess.js:161:1748624) at nUt.$resolveCustomEditor (file:///usr/share/cursor/resources/app/out/vs/workbench/api/node/extensionHostProcess.js:161:1736839) at i1e._doInvokeHandler (file:///usr/share/cursor/resources/app/out/vs/workbench/api/node/extensionHostProcess.js:46:125366) at i1e._invokeHandler (file:///usr/share/cursor/resources/app/out/vs/workbench/api/node/extensionHostProcess.js:46:125108) at i1e._receiveRequest (file:///usr/share/cursor/resources/app/out/vs/workbench/api/node/extensionHostProcess.js:46:123822) at i1e._receiveOneMessage (file:///usr/share/cursor/resources/app/out/vs/workbench/api/node/extensionHostProcess.js:46:122698) at Jae.value (file:///usr/share/cursor/resources/app/out/vs/workbench/api/node/extensionHostProcess.js:46:120794) at J._deliver (file:///usr/share/cursor/resources/app/out/vs/workbench/api/node/extensionHostProcess.js:29:2961) at J.fire (file:///usr/share/cursor/resources/app/out/vs/workbench/api/node/extensionHostProcess.js:29:3282) at Do.fire (file:///usr/share/cursor/resources/app/out/vs/workbench/api/node/extensionHostProcess.js:46:10994) at Jae.value (file:///usr/share/cursor/resources/app/out/vs/workbench/api/node/extensionHostProcess.js:673:14540) at J._deliver (file:///usr/share/cursor/resources/app/out/vs/workbench/api/node/extensionHostProcess.js:29:2961) at J.fire (file:///usr/share/cursor/resources/app/out/vs/workbench/api/node/extensionHostProcess.js:29:3282) at Do.fire (file:///usr/share/cursor/resources/app/out/vs/workbench/api/node/extensionHostProcess.js:46:10994) at MessagePortMain. (file:///usr/share/cursor/resources/app/out/vs/workbench/api/node/extensionHostProcess.js:673:12739) at MessagePortMain.emit (node:events:519:28) at MessagePortMain._internalPort.emit (node:electron/js2c/utility_init:2:2949) Error: Unable to retrieve document from URI 'file:///home/kwickell/code/Playpilot/n8n/memory-bank/activeContext.md' workbench.desktop.main.js:55 ERR cbu: Assertion Failed: Argument is `undefined` or `null`. at zg (vscode-file://vscode-app/usr/share/cursor/resources/app/out/vs/workbench/workbench.desktop.main.js:29:246) at ec (vscode-file://vscode-app/usr/share/cursor/resources/app/out/vs/workbench/workbench.desktop.main.js:29:1268) at pB.resolve (vscode-file://vscode-app/usr/share/cursor/resources/app/out/vs/workbench/workbench.desktop.main.js:4966:9286) at async jqe.setInput (vscode-file://vscode-app/usr/share/cursor/resources/app/out/vs/workbench/workbench.desktop.main.js:4965:10537) at async qzn.doSetInput (vscode-file://vscode-app/usr/share/cursor/resources/app/out/vs/workbench/workbench.desktop.main.js:810:63891) at async qzn.doOpenEditor (vscode-file://vscode-app/usr/share/cursor/resources/app/out/vs/workbench/workbench.desktop.main.js:810:61632) at async qzn.openEditor (vscode-file://vscode-app/usr/share/cursor/resources/app/out/vs/workbench/workbench.desktop.main.js:810:60557) at async vscode-file://vscode-app/usr/share/cursor/resources/app/out/vs/workbench/workbench.desktop.main.js:922:37085 at async $Dt.value (vscode-file://vscode-app/usr/share/cursor/resources/app/out/vs/workbench/workbench.desktop.main.js:938:46814) ``` ---
**Author:** ![Alexandre\_Lavallee](https://avatars.discourse-cdn.com/v4/letter/a/87869e/32.png) [@Alexandre\_Lavallee](https://forum.cursor.com/u/Alexandre_Lavallee)\ **Post date:** [November 11, 2025, 11:30am UTC](https://forum.cursor.com/t/create-update-md-files-unable-to-open-assertion-failed-argument-is-undefined-or-null/140018/17 "2025-11-11T11:30:06Z")
same problem here, i’m on Mac as well, is there a fix already ? it’s quite painful ---
**Author:** ![gap\_acgiu](https://avatars.discourse-cdn.com/v4/letter/g/49beb7/32.png) [@gap\_acgiu](https://forum.cursor.com/u/gap_acgiu)\ **Post date:** [November 12, 2025, 7:26am UTC](https://forum.cursor.com/t/create-update-md-files-unable-to-open-assertion-failed-argument-is-undefined-or-null/140018/18 "2025-11-12T07:26:56Z")
worked, Cursor should display a better error message for debugging ---
**Author:** ![JP\_Harrison](https://avatars.discourse-cdn.com/v4/letter/j/9fc348/32.png) [@JP\_Harrison](https://forum.cursor.com/u/JP_Harrison)\ **Post date:** [November 17, 2025, 2:51pm UTC](https://forum.cursor.com/t/create-update-md-files-unable-to-open-assertion-failed-argument-is-undefined-or-null/140018/19 "2025-11-17T14:51:44Z")
same problem! Tried clearing cache, no Office Viewr extension. MD loads in text Editor but not MD Preview. ---
**Author:** ![Emmanuel\_Cohen](https://avatars.discourse-cdn.com/v4/letter/e/b9e5f3/32.png) [@Emmanuel\_Cohen](https://forum.cursor.com/u/Emmanuel_Cohen)\ **Post date:** [November 20, 2025, 5:18pm UTC](https://forum.cursor.com/t/create-update-md-files-unable-to-open-assertion-failed-argument-is-undefined-or-null/140018/20 "2025-11-20T17:18:45Z")
Meanwhile solution : open the .md with text editor, you will see linting errors, ask cursor to correct them ---
**Author:** ![fox](https://avatars.discourse-cdn.com/v4/letter/f/c5a1d2/32.png) [@fox](https://forum.cursor.com/u/fox)\ **Post date:** [November 23, 2025, 10:16pm UTC](https://forum.cursor.com/t/create-update-md-files-unable-to-open-assertion-failed-argument-is-undefined-or-null/140018/21 "2025-11-23T22:16:56Z")
Can also confirm that opening directly in edit mode works, but it’s very cumbersome (go to file pane, right click, `open with`, then select `text editor`) [Next page](https://forum.cursor.com/t/create-update-md-files-unable-to-open-assertion-failed-argument-is-undefined-or-null/140018.md?page=2)