invokes TouchWorksMagicConstants.ACTION_GET_DOCUMENTS action
        :return: JSON response

def get_documents(self, ehr_username, patient_id, start_date=None,
                      end_date=None, document_id=None, doc_type=None,
                      newest_document='N'):
        """
        invokes TouchWorksMagicConstants.ACTION_GET_DOCUMENTS action
        :return: JSON response
        """

        if not start_date:
            start_date = ''
        if not end_date:
            end_date = ''
        if not doc_type:
            doc_type = ''
        magic = self._magic_json(action=TouchWorksMagicConstants.ACTION_GET_DOCUMENTS,
                                 user_id=ehr_username, token=self._token.token,
                                 patient_id=patient_id,
                                 app_name=self._app_name,
                                 parameter1=start_date,
                                 parameter2=end_date,
                                 parameter3=document_id,
                                 parameter4=doc_type,
                                 parameter5=newest_document)
        response = self._http_request(TouchWorksEndPoints.MAGIC_JSON, data=magic)
        result = self._get_results_or_raise_if_magic_invalid(
            magic,
            response,
            TouchWorksMagicConstants.RESULT_GET_DOCUMENTS)
        return result