Contents API (PUT) and branch listing return generic 500 on repositories with zero commits #8396

Summary

Both PUT /repos/:owner/:repo/contents/* (create/update a file) and GET /repos/:owner/:repo/branches return a generic 500 error on a repository that has no commits yet (e.g. created via POST /user/repos with auto_init: false), instead of a meaningful error or a graceful empty result.

Reproduction

1. Create a repository without an initial commit (auto_init: false, or any other means of creating an empty repo).
2. Call PUT /repos/:owner/:repo/contents/README.md with a minimal body ({"message": "init", "content": "aGVsbG8="}).
3. Observe:

   500 {"message":"Something went wrong, please check the server logs for more information.","url":"https://github.com/gogs/docs-api"}
   

4. Similarly, GET /repos/:owner/:repo/branches on the same repository also returns a generic 500.

Expected behavior

• PUT contents: either successfully create the first commit, or return a clear, typed error (e.g. a 4xx with an explanatory message) instead of a generic 500.
• GET branches: return an empty array [] for a repository with no branches, rather than erroring.

Likely cause

UpdateRepoFile (internal/database/repo_editor.go) calls r.UpdateLocalCopyBranch(opts.OldBranch), which assumes OldBranch (the repository's default branch) already exists. On a repository with zero commits there is no such branch, so the underlying git operation fails and the error surfaces as a generic 500 rather than a handled/typed error.

Environment

• Gogs version: 0.14.3
• Reported while building an MCP (Model Context Protocol) server against the Gogs API: https://github.com/f-3-l-i-x/gogs-mcp-server