code: public Commit getMergeBase(Object projectIdOrPath, List<String> refs) throws GitLabApiException {
          GitLabApiForm queryParams = new GitLabApiForm().withParam("refs", refs, true);
          Response response = get(Response.Status.OK, queryParams.asMap(), "projects",
                  getProjectIdOrPath(projectIdOrPath), "repository", "merge_base");
          return (response.readEntity(Commit.class));
      }
docs: Get the common ancestor for 2 or more refs (commit SHAs, branch names or tags).
  
  <pre><code>GitLab Endpoint: GET /projects/:id/repository/merge_base</code></pre>
  
  @param projectIdOrPath the project in the form of an Integer(ID), String(path), or Project instance
  @param refs a List of 2 or more refs (commit SHAs, branch names or tags)
  @return the Commit instance containing the common ancestor
  @throws GitLabApiException if any exception occurs