Make J2CL super-source'd classes pass nullness checking.

RELNOTES=n/a
PiperOrigin-RevId: 601121536

guava-gwt/src-super/com/google/common/collect/super/com/google/common/collect/DescendingMultiset.java

@@ -150,6 +150,7 @@ public Iterator<E> iterator() {
   }
 
   @Override
+  @SuppressWarnings("nullness") // b/192354773 in our checker affects toArray declarations
   public <T extends @Nullable Object> T[] toArray(T[] array) {
     return standardToArray(array);
   }

guava-gwt/src-super/com/google/common/collect/super/com/google/common/collect/ForwardingImmutableMap.java

@@ -92,12 +92,14 @@ public boolean contains(@Nullable Object object) {
           }
 
           @Override
+          @SuppressWarnings("nullness") // b/192354773 in our checker affects toArray declarations
           public <T extends @Nullable Object> T[] toArray(T[] array) {
             T[] result = super.toArray(array);
             if (size() < result.length) {
               // It works around a GWT bug where elements after last is not
               // properly null'ed.
-              result[size()] = null;
+              @Nullable Object[] unsoundlyCovariantArray = result;
+              unsoundlyCovariantArray[size()] = null;
             }
             return result;
           }

guava-gwt/src-super/com/google/common/collect/super/com/google/common/collect/ImmutableSortedMap.java

@@ -484,7 +484,9 @@ public ImmutableSortedMap<K, V> tailMap(K fromKey) {
     return newView(sortedDelegate.tailMap(fromKey));
   }
 
-  public ImmutableSortedMap<K, V> tailMap(K fromKey, boolean inclusive) {
+  public ImmutableSortedMap<K, V> tailMap(K fromKeyParam, boolean inclusive) {
+    // Declare a "true" local variable so that the Checker Framework will infer nullness.
+    K fromKey = fromKeyParam;
     checkNotNull(fromKey);
     if (!inclusive) {
       fromKey = higher(fromKey);
@@ -522,6 +524,6 @@ private static <K, V> SortedMap<K, V> newModifiableDelegate(Comparator<? super K
   }
 
   private static <E> Comparator<@Nullable E> nullAccepting(Comparator<E> comparator) {
-    return Ordering.from(comparator).nullsFirst();
+    return Ordering.from(comparator).<E>nullsFirst();
   }
 }

guava-gwt/src-super/com/google/common/collect/super/com/google/common/collect/ImmutableSortedSet.java

@@ -262,10 +262,18 @@ public UnmodifiableIterator<E> iterator() {
 
   @Override
   public Object[] toArray() {
-    return ObjectArrays.toArrayImpl(this);
+    /*
+     * ObjectArrays.toArrayImpl returns `@Nullable Object[]` rather than `Object[]` but only because
+     * it can be used with collections that may contain null. This collection is a collection of
+     * non-null elements, so we can treat it as a plain `Object[]`.
+     */
+    @SuppressWarnings("nullness")
+    Object[] result = ObjectArrays.toArrayImpl(this);
+    return result;
   }
 
   @Override
+  @SuppressWarnings("nullness") // b/192354773 in our checker affects toArray declarations
   public <T extends @Nullable Object> T[] toArray(T[] other) {
     return ObjectArrays.toArrayImpl(this, other);
   }