fix(gitlab): Invalid arguments error when using v4 API for gitlab.com

[francovp]

Description

Make merged property "optional" and diff_refs "nullable" in the GitLabMergeRequestSchema to align with GitLab V4 API response.

This fixes the error Invalid arguments: merged: Required, diff_refs: Expected object, received null when creating a merge request using create_merge_request tool.

Cursor example:

Server Details

• Server: gitlab
• Changes to: tools

Motivation and Context

The current version throws an error when parsing the API response when using the V4 API when creating a merge request on gitlab.com, and I need it to use the MCP server with my gitlab repository.

How Has This Been Tested?

Installed the Gitlab MCP Server with envar GITLAB_API_URL=https://gitlab.com/api/v4 on Cursor and asking the Cursor agent to create a Merge Request.

Breaking Changes

No

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Protocol Documentation
• My changes follows MCP security best practices
• I have updated the server's README accordingly
• I have tested this with an LLM client
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have documented all environment variables and configuration options

Additional context