Deleting the last node requires us to set a second to last node as the new last node. Also, the newly created last node should not have any next reference. The code sample is shown here:

    public function deleteLast() { 
        if ($this->_lastNode !== NULL) { 

            $currentNode = $this->_lastNode; 
            if ($currentNode->prev === NULL) { 
                $this->_firstNode = NULL; 
                $this->_lastNode = NULL; 
            } else { 
                $previousNode = $currentNode->prev; 
                $this->_lastNode = $previousNode; 
                $previousNode->next = NULL; 
                $this->_totalNode--; 
                return TRUE; 
            } 
        } 
        return FALSE; 
    }