Why null values are allowed inside java List

Question

If I am writing

List<String> list1 = new ArrayList<String>();
list1.add(null);
list1.add(null);

Java allows that . Why ?? Any use of list1[0] will any way result into NPE .

Answer 1

Java allows that. Why?

Because the List is a collection of object references. Since null is a valid reference (for all types), then the compiler allows statements like list1.add(null)