final protected function where_not_null($column, $or = false){
        $this->_wheres[] = [$this->and_or($or), sprintf("%s IS NOT NULL", $this->escape_column_name($column))];
        return $this;
    }
final protected function where_not_null($column, $or = false){
        $this->_wheres[] = [$this->and_or($or), sprintf("%s IS NOT NULL", $this->escape_column_name($column))];
        return $this;
    }
final protected function where_not_null ( $ column , $ or = false ) { $ this -> _wheres [ ] = [ $ this -> and_or ( $ or ) , sprintf ( "%s IS NOT NULL" , $ this -> escape_column_name ( $ column ) ) ] ; return $ this ; }
Add where not null clause

@param string $column
@param bool $or Default false
@return $this
Add where not null clause