NEED HELP FOR ETAG

Hi Experts ,

Currently the scenario is that we are using standard services for app implemantation and we are facing some error in a class /UI5/CL_UI5_APP_HTTP_HANDLER ----> Method CHECK_304_NOT_MODIFIED ------>

IF lv_old_etag IS INITIAL. RETURN. ENDIF.

   lv_string = iv_etag.

   lv_length_etag = STRLEN( iv_etag ).

   lv_old_etag = lv_old_etag+3(lv_length_etag).

So for resolving this error what shall we do ?

Thank you