docs: public com.squareup.okhttp.Call postCharactersCharacterIdMailLabelsAsync(Integer characterId, String datasource,
              String token, MailLabelSimple mailLabelSimple, final ApiCallback<Integer> callback) throws ApiException {
  
          com.squareup.okhttp.Call call = postCharactersCharacterIdMailLabelsValidateBeforeCall(characterId, datasource,
                  token, mailLabelSimple, callback);
          Type localVarReturnType = new TypeToken<Integer>() {
          }.getType();
          apiClient.executeAsync(call, localVarReturnType, callback);
          return call;
      }