diff --git a/src/java.base/share/classes/java/util/Collections.java b/src/java.base/share/classes/java/util/Collections.java
index ff724198966..3fb41218f4c 100644
--- a/src/java.base/share/classes/java/util/Collections.java
+++ b/src/java.base/share/classes/java/util/Collections.java
@@ -1173,7 +1173,7 @@ public Stream<E> parallelStream() {
      * @since 21
      */
     @SuppressWarnings("unchecked")
-    public static <T> SequencedCollection<T> unmodifiableSequencedCollection(SequencedCollection<? extends T> c) {
+    public static <T extends @Nullable Object> SequencedCollection<T> unmodifiableSequencedCollection(SequencedCollection<? extends T> c) {
         if (c.getClass() == UnmodifiableSequencedCollection.class) {
             return (SequencedCollection<T>) c;
         }
@@ -1283,7 +1283,7 @@ static class UnmodifiableSet<E extends @Nullable Object> extends UnmodifiableCol
      * @since 21
      */
     @SuppressWarnings("unchecked")
-    public static <T> SequencedSet<T> unmodifiableSequencedSet(SequencedSet<? extends T> s) {
+    public static <T extends @Nullable Object> SequencedSet<T> unmodifiableSequencedSet(SequencedSet<? extends T> s) {
         // Not checking for subclasses because of heap pollution and information leakage.
         if (s.getClass() == UnmodifiableSequencedSet.class) {
             return (SequencedSet<T>) s;
@@ -2004,7 +2004,7 @@ && eq(e.getKey(),   t.getKey())
      * @since 21
      */
     @SuppressWarnings("unchecked")
-    public static <K,V> SequencedMap<K,V> unmodifiableSequencedMap(SequencedMap<? extends K, ? extends V> m) {
+    public static <K extends @Nullable Object,V extends @Nullable Object> SequencedMap<K,V> unmodifiableSequencedMap(SequencedMap<? extends K, ? extends V> m) {
         // Not checking for subclasses because of heap pollution and information leakage.
         if (m.getClass() == UnmodifiableSequencedMap.class) {
             return (SequencedMap<K,V>) m;
@@ -6139,7 +6139,7 @@ private void readObjectNoData() throws java.io.ObjectStreamException {
      * @throws IllegalArgumentException if {@code map} is not empty
      * @since 21
      */
-    public static <E> SequencedSet<E> newSequencedSetFromMap(SequencedMap<E, Boolean> map) {
+    public static <E extends @Nullable Object> SequencedSet<E> newSequencedSetFromMap(SequencedMap<E, Boolean> map) {
         if (! map.isEmpty()) // implicit null check
             throw new IllegalArgumentException("Map is non-empty");
         return new SequencedSetFromMap<>(map);
diff --git a/src/java.base/share/classes/java/util/LinkedHashMap.java b/src/java.base/share/classes/java/util/LinkedHashMap.java
index fdebc39c0d6..d9b72f3c1b7 100644
--- a/src/java.base/share/classes/java/util/LinkedHashMap.java
+++ b/src/java.base/share/classes/java/util/LinkedHashMap.java
@@ -393,7 +393,7 @@ void afterNodeAccess(Node<K,V> e) {
      *
      * @since 21
      */
-    public V putFirst(K k, V v) {
+    public @Nullable V putFirst(K k, V v) {
         try {
             putMode = PUT_FIRST;
             return this.put(k, v);
@@ -410,7 +410,7 @@ public V putFirst(K k, V v) {
      *
      * @since 21
      */
-    public V putLast(K k, V v) {
+    public @Nullable V putLast(K k, V v) {
         try {
             putMode = PUT_LAST;
             return this.put(k, v);
diff --git a/src/java.base/share/classes/java/util/SortedMap.java b/src/java.base/share/classes/java/util/SortedMap.java
index 7a92288003e..879171dcfcc 100644
--- a/src/java.base/share/classes/java/util/SortedMap.java
+++ b/src/java.base/share/classes/java/util/SortedMap.java
@@ -305,7 +305,7 @@ public interface SortedMap<K extends @Nullable Object,V extends @Nullable Object
      * @throws UnsupportedOperationException always
      * @since 21
      */
-     default V putFirst(K k, V v) {
+     default @Nullable V putFirst(K k, V v) {
         throw new UnsupportedOperationException();
     }
 
@@ -320,7 +320,7 @@ default V putFirst(K k, V v) {
      * @throws UnsupportedOperationException always
      * @since 21
      */
-    default V putLast(K k, V v) {
+    default @Nullable V putLast(K k, V v) {
         throw new UnsupportedOperationException();
     }
 
diff --git a/src/java.base/share/classes/java/util/TreeMap.java b/src/java.base/share/classes/java/util/TreeMap.java
index 9f65dec28a3..9f4da2f7169 100644
--- a/src/java.base/share/classes/java/util/TreeMap.java
+++ b/src/java.base/share/classes/java/util/TreeMap.java
@@ -329,7 +329,7 @@ public  K lastKey() {
      * @throws UnsupportedOperationException always
      * @since 21
      */
-     public V putFirst(K k, V v) {
+     public @Nullable V putFirst(K k, V v) {
         throw new UnsupportedOperationException();
     }
 
@@ -341,7 +341,7 @@ public V putFirst(K k, V v) {
      * @throws UnsupportedOperationException always
      * @since 21
      */
-    public V putLast(K k, V v) {
+    public @Nullable V putLast(K k, V v) {
         throw new UnsupportedOperationException();
     }
 
diff --git a/src/java.base/share/classes/java/util/concurrent/ConcurrentSkipListMap.java b/src/java.base/share/classes/java/util/concurrent/ConcurrentSkipListMap.java
index 9b05e30e7ed..7784a76b842 100644
--- a/src/java.base/share/classes/java/util/concurrent/ConcurrentSkipListMap.java
+++ b/src/java.base/share/classes/java/util/concurrent/ConcurrentSkipListMap.java
@@ -1896,7 +1896,7 @@ public K lastKey() {
      * @throws UnsupportedOperationException always
      * @since 21
      */
-     public V putFirst(K k, V v) {
+     public @Nullable V putFirst(K k, V v) {
         throw new UnsupportedOperationException();
     }
 
@@ -1908,7 +1908,7 @@ public V putFirst(K k, V v) {
      * @throws UnsupportedOperationException always
      * @since 21
      */
-    public V putLast(K k, V v) {
+    public @Nullable V putLast(K k, V v) {
         throw new UnsupportedOperationException();
     }