code: public MailLabelsResponse getCharactersCharacterIdMailLabels(Integer characterId, String datasource,
              String ifNoneMatch, String token) throws ApiException {
          ApiResponse<MailLabelsResponse> resp = getCharactersCharacterIdMailLabelsWithHttpInfo(characterId, datasource,
                  ifNoneMatch, token);
          return resp.getData();
      }
docs: Get mail labels and unread counts Return a list of the users mail labels,
  unread counts for each label and a total unread count. --- This route is
  cached for up to 30 seconds SSO Scope: esi-mail.read_mail.v1
  
  @param characterId
  An EVE character ID (required)
  @param datasource
  The server name you would like data from (optional, default to
  tranquility)
  @param ifNoneMatch
  ETag from a previous request. A 304 will be returned if this
  matches the current ETag (optional)
  @param token
  Access token to use if unable to set a header (optional)
  @return MailLabelsResponse
  @throws ApiException
  If fail to call the API, e.g. server error or cannot
  deserialize the response body