Fix example implementation for linked-list after extra tests were added (exercism#2344)

sanderploegsma · web-flow · commit 49a150ffef9c · 2023-08-28T20:42:15.000+02:00
diff --git a/exercises/practice/linked-list/.meta/src/reference/java/DoublyLinkedList.java b/exercises/practice/linked-list/.meta/src/reference/java/DoublyLinkedList.java
@@ -16,6 +16,10 @@ void push(T value) {
     }
 
     T pop() {
+        if (head == null) {
+            return null;
+        }
+
         head = head.prev;
         return shift();
     }
@@ -26,6 +30,10 @@ void unshift(T value) {
     }
 
     T shift() {
+        if (head == null) {
+            return null;
+        }
+
         T value = head.value;
 
         Element<T> newHead = head.next;
