}

    @SuppressWarnings("nullness") // TODO: b/423853632 - Remove after checker is fixed.
    @Override
    public @Nullable V merge(
        K key,
        @NonNull V value,
        BiFunction<? super @NonNull V, ? super @NonNull V, ? extends @Nullable V>
            remappingFunction) {
      synchronized (mutex) {
        return delegate().merge(key, value, remappingFunction);
      }
    }

        new ListFuture<V>(ImmutableList.copyOf(futures), true);
    // allAsList ensures that it fills the output list with V instances.
    @SuppressWarnings("nullness")
    ListenableFuture<List<V>> nonNull = nullable;
    return nonNull;
  }

  /**
   * Creates a new {@code ListenableFuture} whose value is a list containing the values of all its
   * input futures, if all succeed.
   *

import java.util.Iterator;
import java.util.List;
import java.util.NoSuchElementException;
import java.util.Objects;
import java.util.PriorityQueue;
import java.util.Queue;
import org.jspecify.annotations.NonNull;
import org.jspecify.annotations.Nullable;

/**
 * This class contains static utility methods that operate on or return objects of type {@link

import java.util.Iterator;
import java.util.List;
import java.util.NoSuchElementException;
import java.util.Objects;
import java.util.PriorityQueue;
import java.util.Queue;
import org.jspecify.annotations.NonNull;
import org.jspecify.annotations.Nullable;

/**
 * This class contains static utility methods that operate on or return objects of type {@link

     */
    public ImmutableSet<@NonNull E> immutableCopy() {
      // Not using ImmutableSet.copyOf() to avoid iterating thrice (isEmpty, size, iterator).
      int maxSize = maxSize();
      if (maxSize == 0) {
        return ImmutableSet.of();
      }
      ImmutableSet.Builder<@NonNull E> builder = ImmutableSet.builderWithExpectedSize(maxSize);
      for (E element : this) {

     */
    public ImmutableSet<@NonNull E> immutableCopy() {
      // Not using ImmutableSet.copyOf() to avoid iterating thrice (isEmpty, size, iterator).
      int maxSize = maxSize();
      if (maxSize == 0) {
        return ImmutableSet.of();
      }
      ImmutableSet.Builder<@NonNull E> builder = ImmutableSet.builderWithExpectedSize(maxSize);
      for (E element : this) {

    public void test_tryStartOperation_singleArg_delegatesToTwoArg() {
        // tryStartOperation(name) should delegate to tryStartOperation(name, null)
        final AtomicReference<String> passedData = new AtomicReference<>("NOT_NULL");
        final CoordinatorHelper helper = new CoordinatorHelper() {
            @Override
            public boolean tryStartOperation(final String operationName, final String data) {
                passedData.set(data);