source/Application/Controller/Admin/ContentList.php
protected function _prepareWhereQuery($aWhere, $sqlFull)
    {
        $sQ = parent::_prepareWhereQuery($aWhere, $sqlFull);
        $sFolder = \OxidEsales\Eshop\Core\Registry::getConfig()->getRequestParameter('folder');
        $sViewName = getviewName("oxcontents");

        //searchong for empty oxfolder fields
        if ($sFolder == 'CMSFOLDER_NONE' || $sFolder == 'CMSFOLDER_NONE_RR') {
            $sQ .= " and {$sViewName}.oxfolder = '' ";
        } elseif ($sFolder && $sFolder != '-1') {
            $sFolder = \OxidEsales\Eshop\Core\DatabaseProvider::getDb()->quote($sFolder);
            $sQ .= " and {$sViewName}.oxfolder = {$sFolder}";
        }

        return $sQ;
    }
protected function _prepareWhereQuery($aWhere, $sqlFull)
    {
        $sQ = parent::_prepareWhereQuery($aWhere, $sqlFull);
        $sFolder = \OxidEsales\Eshop\Core\Registry::getConfig()->getRequestParameter('folder');
        $sViewName = getviewName("oxcontents");

        //searchong for empty oxfolder fields
        if ($sFolder == 'CMSFOLDER_NONE' || $sFolder == 'CMSFOLDER_NONE_RR') {
            $sQ .= " and {$sViewName}.oxfolder = '' ";
        } elseif ($sFolder && $sFolder != '-1') {
            $sFolder = \OxidEsales\Eshop\Core\DatabaseProvider::getDb()->quote($sFolder);
            $sQ .= " and {$sViewName}.oxfolder = {$sFolder}";
        }

        return $sQ;
    }
protected function _prepareWhereQuery ( $ aWhere , $ sqlFull ) { $ sQ = parent :: _prepareWhereQuery ( $ aWhere , $ sqlFull ) ; $ sFolder = \ OxidEsales \ Eshop \ Core \ Registry :: getConfig ( ) -> getRequestParameter ( 'folder' ) ; $ sViewName = getviewName ( "oxcontents" ) ; //searchong for empty oxfolder fields if ( $ sFolder == 'CMSFOLDER_NONE' || $ sFolder == 'CMSFOLDER_NONE_RR' ) { $ sQ .= " and {$sViewName}.oxfolder = '' " ; } elseif ( $ sFolder && $ sFolder != '-1' ) { $ sFolder = \ OxidEsales \ Eshop \ Core \ DatabaseProvider :: getDb ( ) -> quote ( $ sFolder ) ; $ sQ .= " and {$sViewName}.oxfolder = {$sFolder}" ; } return $ sQ ; }
Adding folder check and empty folder field check.

@param array  $aWhere  SQL condition array
@param string $sqlFull SQL query string

@return string
Adding folder check and empty folder field check .