assertThrows(NoSuchElementException.class, () -> assertNull(navigableMap.lastKey()));
  }

  @CollectionSize.Require(ONE)
  public void testSingletonMapFirst() {
    assertEquals(a.getKey(), navigableMap.firstKey());
  }

  @CollectionSize.Require(ONE)
  public void testSingletonMapLast() {
    assertEquals(a.getKey(), navigableMap.lastKey());
  }

  @CollectionSize.Require(SEVERAL)
  public void testFirst() {

    assertThrows(NoSuchElementException.class, () -> assertNull(navigableMap.lastKey()));
  }

  @CollectionSize.Require(ONE)
  public void testSingletonMapFirst() {
    assertEquals(a.getKey(), navigableMap.firstKey());
  }

  @CollectionSize.Require(ONE)
  public void testSingletonMapLast() {
    assertEquals(a.getKey(), navigableMap.lastKey());
  }

  @CollectionSize.Require(SEVERAL)
  public void testFirst() {

			<artifactId>fess-crawler</artifactId>
			<version>${project.version}</version>
		</dependency>
		<dependency>
			<groupId>org.lastaflute</groupId>
			<artifactId>lasta-di</artifactId>
			<version>${lasta.di.version}</version>
		</dependency>
		<dependency>
			<groupId>jakarta.transaction</groupId>
			<artifactId>jakarta.transaction-api</artifactId>
			<version>${jakarta.transaction.version}</version>

    @Override
    public K firstKey() {
      assertTrue(Thread.holdsLock(mutex));
      return delegate().firstKey();
    }

    @Override
    public K lastKey() {
      assertTrue(Thread.holdsLock(mutex));
      return delegate().lastKey();
    }

    private static final long serialVersionUID = 0;
  }

  @AndroidIncompatible // test-suite builders
  public static TestSuite suite() {

			<artifactId>fesen-httpclient</artifactId>
			<version>${fesen.httpclient.version}</version>
		</dependency>
		<dependency>
			<groupId>org.lastaflute</groupId>
			<artifactId>lasta-di</artifactId>
			<version>${lasta.di.version}</version>
		</dependency>
		<dependency>
			<groupId>jakarta.transaction</groupId>
			<artifactId>jakarta.transaction-api</artifactId>
			<version>${jakarta.transaction.version}</version>

    return navigableKeySet();
  }

  @Override
  public @Nullable Entry<K, V> lastEntry() {
    return delegate.lastEntry();
  }

  @Override
  public K lastKey() {
    return delegate.lastKey();
  }

  @Override
  public @Nullable Entry<K, V> lowerEntry(K key) {
    return delegate.lowerEntry(checkValid(key));
  }

  @Override
  public @Nullable K lowerKey(K key) {

    unfiltered.put("dog", 5);

    SortedMap<String, Integer> filtered = Maps.filterEntries(unfiltered, CORRECT_LENGTH);
    assertThat(filtered.firstKey()).isEqualTo("banana");
    assertThat(filtered.lastKey()).isEqualTo("cat");
  }

  public void testHeadSubTailMap_filteredMap() {
    SortedMap<String, Integer> unfiltered = createUnfiltered();
    unfiltered.put("apple", 2);
    unfiltered.put("banana", 6);

    return navigableKeySet();
  }

  @Override
  public @Nullable Entry<K, V> lastEntry() {
    return delegate.lastEntry();
  }

  @Override
  public K lastKey() {
    return delegate.lastKey();
  }

  @Override
  public @Nullable Entry<K, V> lowerEntry(K key) {
    return delegate.lowerEntry(checkValid(key));
  }

  @Override
  public @Nullable K lowerKey(K key) {

| Component | Technology |
|-----------|------------|
| Web Framework | LastaFlute (MVC framework) |
| DI Container | Lasta Di |
| Data Access | DBFlute (type-safe ORM for OpenSearch) |
| Search Engine | OpenSearch |
| App Server | Embedded Tomcat |
| Crawler | fess-crawler library |
| Scheduler | Lasta Job |
| Logging | Log4j2 |
| Testing | JUnit 4/5, UTFlute, REST Assured |

## Development Commands

### Setup
```bash

			<groupId>org.lastaflute</groupId>
			<artifactId>lasta-di</artifactId>
			<version>${lasta.di.version}</version>
		</dependency>
		<dependency>
			<groupId>org.lastaflute</groupId>
			<artifactId>lastaflute</artifactId>
			<version>${lastaflute.version}</version>
		</dependency>
		<dependency>
			<groupId>org.lastaflute.html</groupId>
			<artifactId>lasta-taglib</artifactId>