public EmptyIterator() {
        // Default constructor
    }

    /**
     * {@inheritDoc}
     *
     * @see java.util.Iterator#hasNext()
     */
    @Override
    public boolean hasNext() {
        return false;
    }

    /**
     * {@inheritDoc}
     *
     * @see java.util.Iterator#next()
     */
    @Override
    public SmbResource next() {
        return null;
    }

    /**

  public @Nullable Entry<E> firstEntry() {
    Iterator<Entry<E>> entryIterator = entryIterator();
    return entryIterator.hasNext() ? entryIterator.next() : null;
  }

  @Override
  public @Nullable Entry<E> lastEntry() {
    Iterator<Entry<E>> entryIterator = descendingEntryIterator();
    return entryIterator.hasNext() ? entryIterator.next() : null;
  }

  @Override
  public @Nullable Entry<E> pollFirstEntry() {

import com.google.common.collect.testing.testers.CollectionSerializationEqualTester;
import com.google.common.testing.SerializableTester;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashSet;
import java.util.LinkedHashMap;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import junit.framework.TestSuite;

/**

 * either express or implied. See the License for the specific language
 * governing permissions and limitations under the License.
 */
package org.codelibs.fess.entity;

import java.util.HashSet;
import java.util.Set;

import org.codelibs.fess.mylasta.direction.FessConfig;
import org.codelibs.fess.unit.UnitFessTestCase;
import org.codelibs.fess.util.ComponentUtil;

  public @Nullable Entry<E> firstEntry() {
    Iterator<Entry<E>> entryIterator = entryIterator();
    return entryIterator.hasNext() ? entryIterator.next() : null;
  }

  @Override
  public @Nullable Entry<E> lastEntry() {
    Iterator<Entry<E>> entryIterator = descendingEntryIterator();
    return entryIterator.hasNext() ? entryIterator.next() : null;
  }

  @Override
  public @Nullable Entry<E> pollFirstEntry() {

import static org.mockito.Mockito.doNothing;
import static org.mockito.Mockito.doThrow;
import static org.mockito.Mockito.when;

import java.util.Collections;
import java.util.HashSet;
import java.util.Set;

import javax.security.auth.Subject;
import javax.security.auth.kerberos.KerberosKey;
import javax.security.auth.login.LoginContext;
import javax.security.auth.login.LoginException;

        // hasNext/next sequence over two elements
        assertTrue(it.hasNext(), "Expected first element available");
        SmbResource r1 = it.next();
        assertNotNull(r1);
        assertEquals("foo/", r1.getName(), "First child name should match with trailing slash");

        assertTrue(it.hasNext(), "Expected second element available");
        SmbResource r2 = it.next();

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.Reader;
import java.io.StringReader;
import java.util.Base64;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;
import java.util.zip.GZIPInputStream;
import java.util.zip.GZIPOutputStream;

import org.apache.commons.lang3.StringUtils;
import org.apache.logging.log4j.LogManager;

    Iterator<Subscriber> empty = registry.getSubscribers("");
    assertFalse(empty.hasNext());

    empty = registry.getSubscribers("");

    registry.register(s1);
    assertFalse(empty.hasNext());

    Iterator<Subscriber> one = registry.getSubscribers("");
    assertEquals(s1, one.next().target);
    assertFalse(one.hasNext());

    one = registry.getSubscribers("");

    registry.register(s2);

   * and updates {@link #successorIterator} to iterate through the successors of {@link #node}.
   */
  final boolean advance() {
    checkState(!successorIterator.hasNext());
    if (!nodeIterator.hasNext()) {
      return false;
    }
    node = nodeIterator.next();
    successorIterator = graph.successors(node).iterator();
    return true;
  }

  /**