In my C++ project, all classes use linked list class, and when I run the project, it throws a nullptr exception:

I tried to solve the problem with Copilot AI, but it didn’t solve my problem, it provided the debugging throw statements.

The code of my linked list class:

#ifndef LINKEDLIST_H
#define LINKEDLIST_H

#include "Services.h"
#include "Employee.h"
#include "transaction.h"
#include "Citizen.h"
#include <iostream>
using namespace std;

template <typename T>
class Node {
public:
    T data;
    Node* next;
    Node* prev;
    Node(T val) : data(val), next(nullptr), prev(nullptr) {}
};

template <typename T>
class LinkedList {
private:
    Node<T>* head;
    Node<T>* tail;

public:
    LinkedList() : head(nullptr), tail(nullptr) {}

    Node<T>* getHead() { return head; }
    Node<T>* getTail() { return tail; }

    void addHead(T val) {
        Node<T>* newNode = new Node<T>(val);
        if (newNode == nullptr) {
            throw std::runtime_error("Memory allocation failed for newNode.");
        }

        if (head == nullptr) {
            head = tail = newNode;
        } else {
            newNode->next = head;
            head->prev = newNode;
            head = newNode;
        }

        // Debugging statements to ensure head and tail are not nullptr
        if (head == nullptr || tail == nullptr) {
            throw std::runtime_error("Head or Tail is nullptr after adding a new head.");
        }

        if (head->next != nullptr && head->next->prev != head) {
            throw std::runtime_error("Incorrect previous pointer assignment in the linked list.");
        }
    }
};

#endif // LINKEDLIST_H

I used this linked list to implement queue from citizen node and stack from transaction node so my whole project depend on it