C - Segmentation fault when checking if a pointer is NULL

so got this segmentation fault every time I tried to check if a pointer variable is a NULL. The error is from these lines of code in add function:

if (it->head == NULL){
        printf("worksfine");
    }

This is the whole code that I have:

#include<stdio.h>
#include<stdlib.h>
#include<assert.h>

typedef struct Node{
    int val;
    struct Node *prev;
    struct Node *next;
} node;

typedef struct IteratorInt{
    node *head;
    node *tail;
    node *last;
} IteratorInt;

IteratorInt IteratorIntNew(){
    IteratorInt *listint;
    listint = malloc(sizeof(IteratorInt));
    listint->head = NULL;
    listint->tail = NULL;
    listint->last = NULL;
    printf("address made %u\n", listint);
    return *listint;
}

int add(IteratorInt *it, int v){
    node *n;
    n->val = v;
    n->next = NULL;
    n->prev = NULL;
    printf("func works\n");
    printf("n %d\n", n->val);
    printf("address %u", it);
    it->head = n;
    printf("result %d", it->head->val);
    if (it->head == NULL){
        printf("worksfine");
    }
   /* if (it->head == 0){
       it->head = n;
    }
    if (it->tail == 0){
        it->tail = n;
    }
    if (it->last == 0){
        it->last = n;
    }*/

    return 1;
}

int main() {
    IteratorInt lit = IteratorIntNew();
    printf("works %u", &lit);
    add(&lit, 10);

    /*printf("Node value %d\n", lit.head.val);
    add(&lit, 15);
    printf("Node value %d", lit.tail.val);*/
    return 0;
}

Can you tell me what's wrong with it? and how to solve that? Thanks a lot.