The error error: 'main/' does not have a commit checked out occurs when Git tries to add files to a submodule that is in a detached HEAD state or has no checked-out commit. This happens because the main repository expects the submodule to point to a specific commit, but it's in an invalid state.

To fix this, you need to navigate into the submodule's directory and check out a commit, usually by switching to the main branch or a specific branch.

The "refusing to merge unrelated histories" error occurs when you try to merge two branches that do not share a common history. This typically happens when you initialize a new Git repository and then try to pull a remote repository's contents into it, as Git sees them as two completely separate projects.

To solve this, you can use the --allow-unrelated-histories flag. This flag forces Git to merge the two independent histories, creating a merge commit that joins them together.

How to Solve "Not Possible to Fast-Forward" with git pull​

The git pull "Not possible to fast-forward" error happens when your local branch and the remote branch have diverged. This means there are new commits on the remote branch that you don't have, and you also have local commits that are not on the remote branch. Git cannot simply move your branch pointer forward (fast-forward) because doing so would lose your local changes.

To fix this, you must explicitly tell Git how to merge the divergent histories. There are two primary solutions: using git pull with rebase or performing a standard git pull followed by a manual merge.

To save your username and password in Git, you can configure a credential helper. A credential helper is a Git component that securely stores your authentication information in memory or on disk, so you don't have to enter it every time you interact with a remote repository.

The fatal: unable to access error with the message "Write access to repository not granted" typically means you don't have the necessary permissions to push changes to the GitHub repository. It's a clear signal from the server that your authentication credentials, while valid, don't grant you the required write access.

Here's how to diagnose and solve this issue:

Docusaurus doesn't have a built-in feature to create a separate image sitemap. The @docusaurus/plugin-sitemap only handles generating a sitemap for your pages and documentation, not for media like images.

Since the plugin doesn't have a specific option for image sitemaps, the recommended approach is to manually create an XML file that follows the image sitemap protocol and place it in the static directory of your Docusaurus project.

To define a property that can be a string or null in OpenAPI (Swagger), you use different methods depending on the OpenAPI specification version.

To fix a detached HEAD in Git, you need to save your work by creating a new branch or by checking out an existing one. A detached HEAD occurs when you check out a specific commit, tag, or a remote branch's commit instead of a local branch name (1). In this state, any new commits you make are not part of any branch, making them easy to lose.

The HEAD pointer in Git usually points to the tip of a branch (e.g., main, feature-a). A detached HEAD means the pointer is pointing directly to a commit instead of a branch.

Python helper function for making it work both locally and on Vercel is to correctly determine the project's root directory, as Vercel's serverless environment can change the working directory.

The primary cause for import errors on Vercel is often a mismatch between your local development environment's flexibility and Vercel's strict, serverless build process. Beyond the crucial __init__.py file, you need to pay attention to your project's overall structure, the way you write imports, and Vercel's build configuration.