How to implement a Queue using Linked List in C++ by classes only

I have a Linked List class, implemented like this (and tested too):

template <class T>
class LList {
    LNode<T>* head;
    LNode<T>* tail;
    int size; // proporciona muitas vantagens
    LNode<T>* rCopy(LNode<T>* right);
public:
    LList() : head(nullptr), tail(nullptr), size(0) {}
    LList(const LList& other) :
            head(nullptr), tail(nullptr), size(0) {
        *this = other;
    }
    ~LList() { clear(); }

...
    // O(1)
    void insertAtBack(T newvalue) {
        LNode<T>* tmp = new LNode<T>(newvalue, nullptr);
        tail->next = tmp;
        tail = tmp;
        if (head == nullptr)
            head = tmp;
        this->size++;
    }
...
};

Then, I created a Queue class:

template <class T>
class Queue {
private:
    LList<T> lista;
public:
//    Queue() : lista() {} ??? don't know how to do it
    void enqueue(T element);
    T peek();
    void dequeue();
    int size();
    bool isEmpty();
    void sizeLog();
};

template<class T>
void Queue<T>::enqueue(T element) {
    lista.insertAtBack(element);
}

But I can't use it on main, any attempt to enqueue causes crashing in the for loop, that returns error code -1073741819. The function isEmpty() works and displays true.

Queue<int> f;
std::cout << "created" << endl;
std::cout << f.isEmpty() << endl;

for (int i=0; i<10; i++) {
    f.enqueue(i*5);
}

Output:

created
1

Process finished with exit code -1073741819 (0xC0000005)

I've tried to write a constructor for Queue class to initialize the LList class, but can't find the right way to do it. If I write a main function to test only the LList class, I have no need for initialization, because its construtor already carries on with the job.

Initially the tail, head are nullptr so when the first element is inserted, you attempt to access tail->next in insertAtBack where tail is nullptr causing the error (probably an uncaught exception), if the tail is nullptr, simply assign it the tmp value. place a nullptr check for the expression like so..

// O(1)
    void insertAtBack(T newvalue) {
        LNode<T>* tmp = new LNode<T>(newvalue, nullptr);

        // if it is nullptr, 
        // it is the first and only element
        // so head = tail = tmp
        if(tail != nullptr) 
            tail->next = tmp;
        tail = tmp;
        if (head == nullptr)
            head = tmp;
        this->size++;
    }

``