checkNotNull(appendable, "appendable");
        checkNotNull(parts, "parts");
        while (parts.hasNext()) {
          Object part = parts.next();
          if (part != null) {
            appendable.append(Joiner.this.toString(part));
            break;
          }
        }
        while (parts.hasNext()) {
          Object part = parts.next();

  MapsImplEnum mapsImpl;

  /**
   * A map of contents pre-created before experiment starts to only measure map creation cost. The
   * implementation for the creation of contents is independent and could be different from that of
   * the map under test.
   */
  Map<Element, Element> contents;

  /** Map pre-created before experiment starts to only measure iteration cost during experiment. */
  Map<Element, Element> map;

import java.io.Serializable;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * An immutable {@code Map.Entry}, used both by {@link
 * com.google.common.collect.Maps#immutableEntry(Object, Object)} and by other parts of {@code
 * common.collect} as a superclass.
 */
@GwtCompatible(serializable = true)
@ElementTypesAreNonnullByDefault
class ImmutableEntry<K extends @Nullable Object, V extends @Nullable Object>

      @ParametricNullness E fromElement,
      BoundType fromBoundType,
      @ParametricNullness E toElement,
      BoundType toBoundType) {
    // These are checked elsewhere, but NullPointerTester wants them checked eagerly.
    checkNotNull(fromBoundType);
    checkNotNull(toBoundType);
    return tailMultiset(fromElement, fromBoundType).headMultiset(toElement, toBoundType);
  }

  /** Name of FinalizableReference.class. */
  private static final String FINALIZABLE_REFERENCE = "com.google.common.base.FinalizableReference";

  /**
   * Starts the Finalizer thread. FinalizableReferenceQueue calls this method reflectively.
   *
   * @param finalizableReferenceClass FinalizableReference.class.
   * @param queue a reference queue that the thread will poll.

     * We never want to pass null for them, so we haven't annotated them to say that null is
     * allowed. But at the same time, it seems wasteful to bother inserting the checkNotNull calls
     * that NullPointerTester wants.
     *
     * (This empty method disables the automatic null testing provided by PackageSanityTests.)
     */
  }

   * NullPointerException if the comparator does. Since our construction
   * methods ensure that null is never present in the map, it's OK for the
   * comparator to look for it wherever it wants.
   *
   * Note that we do NOT touch the comparator returned by comparator(), which
   * should be identical to the one the user passed in. We touch only the
   * "secret" comparator used by the delegate implementation.

        checkNotNull(appendable, "appendable");
        checkNotNull(parts, "parts");
        while (parts.hasNext()) {
          Object part = parts.next();
          if (part != null) {
            appendable.append(Joiner.this.toString(part));
            break;
          }
        }
        while (parts.hasNext()) {
          Object part = parts.next();

        }
      };

  private static void checkResult(Joiner joiner, Iterable<Integer> parts, String expected) {
    assertEquals(expected, joiner.join(parts));
    assertEquals(expected, joiner.join(parts.iterator()));

    StringBuilder sb1FromIterable = new StringBuilder().append('x');
    joiner.appendTo(sb1FromIterable, parts);
    assertEquals("x" + expected, sb1FromIterable.toString());

  On this the White Rabbit blew three blasts on the trumpet, and
then unrolled the parchment scroll, and read as follows:--

    `The Queen of Hearts, she made some tarts,
          All on a summer day:
      The Knave of Hearts, he stole those tarts,
          And took them quite away!'

  `Consider your verdict,' the King said to the jury.

  `Not yet, not yet!' the Rabbit hastily interrupted.  `There's