// requireNonNull is safe (under the conditions listed in the comment in the branch above).
      KeyList<K, V> keyList = requireNonNull(keyToKeyList.get(node.getKey()));
      keyList.count--;

      if (node.previousSibling == null) {
        // requireNonNull is safe because we checked that not *both* siblings were null.
        keyList.head = requireNonNull(node.nextSibling);
      } else {

      return policy == Policies.DISABLED
          ? new ReentrantLock(fair)
          // requireNonNull is safe because createNodes inserts an entry for every E.
          // (If the caller passes `null` for the `rank` parameter, this will throw, but that's OK.)
          : new CycleDetectingReentrantLock(requireNonNull(lockGraphNodes.get(rank)), fair);
    }

            @Nonnull ArtifactCoordinates artifactCoordinates,
            @Nullable List<RemoteRepository> repositories) {
        return builder()
                .session(requireNonNull(session, "session cannot be null"))
                .artifactCoordinates(requireNonNull(artifactCoordinates, "artifactCoordinates cannot be null"))
                .repositories(repositories)
                .build();
    }

    @Nonnull

import org.apache.maven.api.ProtoSession;
import org.apache.maven.api.annotations.Experimental;
import org.apache.maven.api.annotations.Nonnull;
import org.apache.maven.api.annotations.Nullable;

import static java.util.Objects.requireNonNull;

/**
 * Collects problems that were encountered during project building.
 *
 * @param <P> The type of the problem.
 * @since 4.0.0
 */
@Experimental

       *   modification is undefined, anyway.)
       */
      requireNonNull(rowEntry);
      Entry<C, V> columnEntry = columnIterator.next();
      return immutableCell(rowEntry.getKey(), columnEntry.getKey(), columnEntry.getValue());
    }

    @Override
    public void remove() {
      columnIterator.remove();
      /*
       * requireNonNull is safe because:
       *

              lock.unlock();
            }
          });
    }

    @Override
    protected final void doStop() {
      // Both requireNonNull calls are safe because doStop can run only after a successful doStart.
      requireNonNull(runningTask);
      requireNonNull(executorService);
      runningTask.cancel(false);
      executorService.execute(
          () -> {
            try {
              lock.lock();

import org.apache.maven.api.annotations.Nonnull;
import org.apache.maven.api.annotations.NotThreadSafe;
import org.apache.maven.api.annotations.Nullable;

import static java.util.Objects.requireNonNull;

/**
 *
 * @since 4.0.0
 */
@Experimental
public interface ToolchainsBuilderRequest extends Request<ProtoSession> {

    /**
     * Gets the installation Toolchains source.
     *

     */
    @Nonnull
    static ProjectBuilderRequest build(@Nonnull Session session, @Nonnull Source source) {
        return builder()
                .session(requireNonNull(session, "session cannot be null"))
                .source(requireNonNull(source, "source cannot be null"))
                .build();
    }

    /**
     * Creates a new ProjectBuilderRequest with the specified session and path.
     *

        // TODO(b/139735208): Figure out what to do when the factory returns null.
        requireNonNull(thread);
        if (nameFormat != null) {
          // requireNonNull is safe because we create `count` if (and only if) we have a nameFormat.
          thread.setName(format(nameFormat, requireNonNull(count).getAndIncrement()));
        }
        if (daemon != null) {
          thread.setDaemon(daemon);

package org.apache.maven.api.services;

import org.apache.maven.api.ProtoSession;
import org.apache.maven.api.annotations.Experimental;
import org.apache.maven.api.annotations.Nonnull;

import static java.util.Objects.requireNonNull;

/**
 * Base class for requests.
 *
 * @since 4.0.0
 */
@Experimental
abstract class BaseRequest<S extends ProtoSession> implements Request<S> {

    private final S session;