There should be an else clause on delete(Node n, int key) method for the case where the n.getNext() node does not have the getKey()==key.

https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/hashmap/hashing/HashMap.java

/**
Linked list class - delete method with the following signature
*/
private void delete(Node n, int key) {
if (n.getNext().getKey() == key) {
if (n.getNext().getNext() == null) {
n.setNext(null);
} else {
n.setNext(n.getNext().getNext());
}
}
}

Possible Solution

    private void delete(Node n, int key) {
        if (n.getNext().getKey() == key) {
            if (n.getNext().getNext() == null) {
                n.setNext(null);
            } else {
                n.setNext(n.getNext().getNext());
            }
        }

else{
          delete(n.getNext(),key);
      }

    }