There is no defined term as empty array

Your array will always hold some value even if you dont initialize it explicitly

You need to define in your application how will you term it as empty may be by considering if its(element of array) value is 0 or some other value

std::list::end returns an iterator to the element following the last element of the container, This element acts as a placeholder; attempting to access it results in undefined behavior.

You could use std::list::back or reverse iterator std::list::rbegin

try:

items.back()->getID() +1;
(*items.rbegin())->getID() +1;

you should return theList.
when loop ends currentElement is NULL. so theList will be pointing at the last node.
And make sure that theList received by the function is not NULL.

If you just want to access the last item in the list you can do

if (integerList.Count > 0)
{
   //  pre C#8.0 : var item = integerList[integerList.Count - 1];
   //  C#8.0 : 
   var item = integerList[^1];
}

to get the total number of items in the list you can use the Count property

var itemCount = integerList.Count;

i was trying to get the new second element of the list, using std::next.

You are not getting the new second element of the list, what you are trying to get is the next new address of the list, since what you are passing is the pointer, the address of the list, not the iterator:

list *getNextXValue(list *Head, int x)
{
    return std::next(Head, x);
}

Try this instead:

#include <iostream>
#include <list>

#define LOG(x) std::cout << x << std::endl;

typedef std::list<int> list;

std::list<int>::iterator getNextXValue(std::list<int>::iterator Head, int x) {
  return std::next(Head, x);
}

/**
 * @brief Find last element of a linked list of ints
 *
 * @return int Program ended correctly
 */
int main() {
  list listOne;
  list *aux = NULL;

  // Inserts all the elements in the list
  for (int i = 0; i < 100; i++) {
    listOne.insert(listOne.end(), i);
  }

  listOne.reverse();

  auto next = getNextXValue(listOne.begin(), 1);

  std::cout << *next << std::endl;

  return 0;
}