code: public User setUserAvatar(final Object userIdOrUsername, File avatarFile) throws GitLabApiException {
          Response response = putUpload(Response.Status.OK, "avatar", avatarFile,  "users", getUserIdOrUsername(userIdOrUsername));
          return (response.readEntity(User.class));
      }
docs: Uploads and sets the user's avatar for the specified user.
  
  <pre><code>PUT /users/:id</code></pre>
  
  @param userIdOrUsername the user in the form of an Integer(ID), String(username), or User instance
  @param avatarFile the File instance of the avatar file to upload
  @return the updated User instance
  @throws GitLabApiException if any exception occurs