Modifying objects when passed to methods in Java

Question

I have the following code for removing duplicates from a Linked list and it works perfectly fine. However I have some questions on how it works.

Node.java

public class Node {
    
    int value;
    Node next;
    
    Node(int value) {
        this.value = value;
        this.next = null;
    }

}

RemoveDuplicates.java

public class RemoveDuplicates {


    public static void removeDups(Node head) {

        Node p = null;
        Set<Integer> set = new HashSet<>();

        while(head != null) {

            if(set.add(head.value)) {
                p = head;
            } else {
                p.next = head.next;
            }

            head = head.next; // Shouldn't this set the input node (head) as null in the last iteration?
        }

    }


    public static void main(String[] args) {

        Node n1 = new Node(10);
        Node n2 = new Node(11);
        Node n3 = new Node(11);
        Node n4 = new Node(10);
        Node n5 = new Node(12);

        n1.next = n2;
        n2.next = n3;
        n3.next = n4;
        n4.next = n5;

        removeDups(n1); // Shouldn't n1 be null as we looped thru the end inside the method?

        while(n1 != null) {
            System.out.print(n1.value + " "); // Prints -> 10 11 12
            n1 = n1.next;
        }

        System.out.println(n1 == null); // This returns true
    }

}

1. How does the head node still pointing correctly to the head when looped thru inside the removeDups method?
2. On the other hand when we loop thru it inside the main method, it returns null?