error: comparison of array 'user->friends' equal to a null pointer is always false [-Werror,-Wtautological-pointer-compare]
    if (user->friends == NULL) {
int delete_user(const char *name, User **user_ptr_del) {
    User *user = find_user(name, *user_ptr_del);
    if (user == NULL){
        // if a user with this name does not exist.
        return 1;
    }
    if (user->friends == NULL) {
        // user does not have any friends
        User *current = *user_ptr_del;
        User *prev = NULL;
        while (current != NULL) {
            if (strcmp(current->name, name) == 0) {
                if (prev == NULL) {
                        // The user to delete is at the head of the list
                        *user_ptr_del = current->next;
                    } else {
                        prev->next = current->next;
                    }
                    free(current);
                    return 0;
            }
            prev = current;
            current = current->next;
        }
        return 1;
    }

    // Remove the deleted user from any lists of friends.
    for (int i = 0; i < MAX_FRIENDS; i++){
        if (user->friends[i] != NULL){
            int j = 0;
            while (user->friends[i]->friends[j] != NULL) {
                if (user->friends[i]->friends[j] == user) {
                // Remove the current user from this friend's list
                for (int k = j; k < MAX_FRIENDS - 1; k++) {
                    user->friends[i]->friends[k] = user->friends[i]->friends[k + 1];
                }
                user->friends[i]->friends[MAX_FRIENDS - 1] = NULL;
                break;
            }
            j++;
            }
        }
    }

    // delete the user from the list pointed to by *user_ptr_del
    User *current = *user_ptr_del;
    User *prev = NULL;
    while (current != NULL) {
        if (strcmp(current->name, name) == 0) {
            if (prev == NULL) {
                    // The user to delete is at the head of the list
                    *user_ptr_del = current->next;
                } else {
                    prev->next = current->next;
                }
                free(current);
                return 0;
        }
        prev = current;
        current = current->next;
    }
    return 1;
}