Address a couple nullness errors.

One is from cl/725859649 (I _thought_ I had tested that change with nullness checking on), and the other is from [a change to the annotations for `Map.replace` used by Android](jspecify/jdk#118). (I think that the latter change should actually be leading to _more_ errors in our _other_ implementations of the 3-arg `Map.replace`, like in `Maps` and `Synchronized`. The lack of errors is probably a bug in the checker.)

RELNOTES=n/a
PiperOrigin-RevId: 728229469

android/guava/src/com/google/common/collect/ForwardingConcurrentMap.java

@@ -66,6 +66,7 @@ public boolean remove(@Nullable Object key, @Nullable Object value) {
 
   @CanIgnoreReturnValue
   @Override
+  @SuppressWarnings("nullness") // https://github.com/jspecify/jdk/issues/118
   public boolean replace(K key, V oldValue, V newValue) {
     return delegate().replace(key, oldValue, newValue);
   }

android/guava/src/com/google/common/collect/TreeBasedTable.java

@@ -121,7 +121,9 @@ public static <R, C, V> TreeBasedTable<R, C, V> create(
    */
   public static <R, C, V> TreeBasedTable<R, C, V> create(TreeBasedTable<R, C, ? extends V> table) {
     TreeBasedTable<R, C, V> result =
-        new TreeBasedTable<>(table.rowKeySet().comparator(), table.columnComparator());
+        // requireNonNull is safe, as discussed in rowComparator() below.
+        new TreeBasedTable<>(
+            requireNonNull(table.rowKeySet().comparator()), table.columnComparator());
     result.putAll(table);
     return result;
   }

guava/src/com/google/common/collect/ForwardingConcurrentMap.java

@@ -66,6 +66,7 @@ public boolean remove(@Nullable Object key, @Nullable Object value) {
 
   @CanIgnoreReturnValue
   @Override
+  @SuppressWarnings("nullness") // https://github.com/jspecify/jdk/issues/118
   public boolean replace(K key, V oldValue, V newValue) {
     return delegate().replace(key, oldValue, newValue);
   }

guava/src/com/google/common/collect/TreeBasedTable.java

@@ -121,7 +121,9 @@ public static <R, C, V> TreeBasedTable<R, C, V> create(
    */
   public static <R, C, V> TreeBasedTable<R, C, V> create(TreeBasedTable<R, C, ? extends V> table) {
     TreeBasedTable<R, C, V> result =
-        new TreeBasedTable<>(table.rowKeySet().comparator(), table.columnComparator());
+        // requireNonNull is safe, as discussed in rowComparator() below.
+        new TreeBasedTable<>(
+            requireNonNull(table.rowKeySet().comparator()), table.columnComparator());
     result.putAll(table);
     return result;
   }