Update signature of Map.computeIfAbsent

src/java.base/share/classes/java/util/HashMap.java

@@ -1217,8 +1217,8 @@ public boolean replace(K key, V oldValue, V newValue) {
      * mapping function modified this map
      */
     @Override
-    public V computeIfAbsent(K key,
-                             Function<? super K, ? extends V> mappingFunction) {
+    public @Nullable V computeIfAbsent(K key,
+                             Function<? super K, ? extends @Nullable V> mappingFunction) {
         if (mappingFunction == null)
             throw new NullPointerException();
         int hash = hash(key);

src/java.base/share/classes/java/util/Hashtable.java

@@ -1047,7 +1047,7 @@ public synchronized boolean replace(K key, V oldValue, V newValue) {
      * mapping function modified this map
      */
     @Override
-    public synchronized V computeIfAbsent(K key, Function<? super K, ? extends V> mappingFunction) {
+    public synchronized @Nullable V computeIfAbsent(K key, Function<? super K, ? extends @Nullable V> mappingFunction) {
         Objects.requireNonNull(mappingFunction);
 
         Entry<?,?> tab[] = table;

src/java.base/share/classes/java/util/Map.java

@@ -1081,8 +1081,9 @@ default boolean replace(K key, V oldValue, V newValue) {
      *         ({@linkplain Collection##optional-restrictions optional})
      * @since 1.8
      */
-    default V computeIfAbsent(K key,
-            Function<? super K, ? extends V> mappingFunction) {
+    // We would use an annotation like @PolyNull here if JSpecify offered one.
+    default @Nullable V computeIfAbsent(K key,
+            Function<? super K, ? extends @Nullable V> mappingFunction) {
         Objects.requireNonNull(mappingFunction);
         V v;
         if ((v = get(key)) == null) {

src/java.base/share/classes/java/util/Properties.java

@@ -1502,8 +1502,8 @@ public synchronized boolean replace(Object key, Object oldValue, Object newValue
     }
 
     @Override
-    public synchronized Object computeIfAbsent(Object key,
-            Function<? super Object, ? extends Object> mappingFunction) {
+    public synchronized @Nullable Object computeIfAbsent(Object key,
+            Function<? super Object, ? extends @Nullable Object> mappingFunction) {
         return map.computeIfAbsent(key, mappingFunction);
     }
 

src/java.base/share/classes/java/util/TreeMap.java

@@ -595,7 +595,7 @@ final Entry<K,V> getLowerEntry(K key) {
      * mapping function modified this map
      */
     @Override
-    public V computeIfAbsent(K key, Function<? super K, ? extends V> mappingFunction) {
+    public @Nullable V computeIfAbsent(K key, Function<? super K, ? extends @Nullable V> mappingFunction) {
         Objects.requireNonNull(mappingFunction);
         V newValue;
         Entry<K,V> t = root;

src/java.base/share/classes/java/util/concurrent/ConcurrentHashMap.java

@@ -1725,7 +1725,7 @@ boolean removeValueIf(Predicate<? super V> function) {
      * @throws RuntimeException or Error if the mappingFunction does so,
      *         in which case the mapping is left unestablished
      */
-    public V computeIfAbsent(K key, Function<? super K, ? extends V> mappingFunction) {
+    public @Nullable V computeIfAbsent(K key, Function<? super K, ? extends @Nullable V> mappingFunction) {
         if (key == null || mappingFunction == null)
             throw new NullPointerException();
         int h = spread(key.hashCode());

src/java.base/share/classes/java/util/concurrent/ConcurrentMap.java

@@ -328,8 +328,8 @@ default void replaceAll(BiFunction<? super K, ? super V, ? extends V> function)
      * @since 1.8
      */
     @Override
-    default V computeIfAbsent(K key,
-            Function<? super K, ? extends V> mappingFunction) {
+    default @Nullable V computeIfAbsent(K key,
+            Function<? super K, ? extends @Nullable V> mappingFunction) {
         Objects.requireNonNull(mappingFunction);
         V oldValue, newValue;
         return ((oldValue = get(key)) == null

src/java.base/share/classes/java/util/concurrent/ConcurrentSkipListMap.java

@@ -1463,8 +1463,8 @@ else if ((d = h.down) != null)    // remove levels
      *         or the mappingFunction is null
      * @since 1.8
      */
-    public V computeIfAbsent(K key,
-                             Function<? super K, ? extends V> mappingFunction) {
+    public @Nullable V computeIfAbsent(K key,
+                             Function<? super K, ? extends @Nullable V> mappingFunction) {
         if (key == null || mappingFunction == null)
             throw new NullPointerException();
         V v, p, r;