code: public Member addMember(Object groupIdOrPath, Integer userId, AccessLevel accessLevel, Date expiresAt) throws GitLabApiException {
          return (addMember(groupIdOrPath, userId, accessLevel.toValue(), expiresAt));
      }
docs: Adds a user to the list of group members.
  
  <pre><code>GitLab Endpoint: POST /groups/:id/members</code></pre>
  
  @param groupIdOrPath the group ID, path of the group, or a Group instance holding the group ID or path, required
  @param userId the user ID of the member to add, required
  @param accessLevel the access level for the new member, required
  @param expiresAt the date the membership in the group will expire, optional
  @return a Member instance for the added user
  @throws GitLabApiException if any exception occurs