Just edit below portion of the function _json_response defined at odoo/odoo11/odoo/http.py near about line no : 621-630 as below

    def _json_response(self, result=None, error=None):

        response = {
            'jsonrpc': '2.0',
            'id': self.jsonrequest.get('id')
            }
        if error is not None:
            response['error'] = error
        if result is not None:
            response['result'] = result

to new:

    def _json_response(self, result=None, error=None):

        response = {}
        if error is not None:
            response = error
        if result is not None:
            response = result
Please do the procedure at your own risk. these procedure isn't a recommended procedure.