*
   * <p><b>Discouraged:</b> Prefer using either {@code x -> x == null} or {@code Objects::isNull},
   * but note that lambdas and method references do not have human-readable {@link #toString()}
   * representations and are not serializable.
   */
  public static <T extends @Nullable Object> Predicate<T> isNull() {
    return ObjectPredicate.IS_NULL.withNarrowedType();
  }

  /**

   *
   * <p><b>Discouraged:</b> Prefer using either {@code x -> x == null} or {@code Objects::isNull},
   * but note that lambdas and method references do not have human-readable {@link #toString()}
   * representations and are not serializable.
   */
  public static <T extends @Nullable Object> Predicate<T> isNull() {
    return ObjectPredicate.IS_NULL.withNarrowedType();
  }

  /**

    assertThat(map.getInstance(Integer.class)).isNull();

    map.putInstance(Long.class, null);
    assertTrue(map.containsKey(TypeToken.of(Long.class)));
    assertTrue(map.entrySet().contains(immutableEntry(TypeToken.of(Long.class), null)));
    assertThat(map.get(TypeToken.of(Long.class))).isNull();
    assertThat(map.getInstance(Long.class)).isNull();
  }

	}
	// check empty or full
	if rb.IsEmpty() {
		t.Fatalf("expect IsEmpty is false but got true")
	}
	if rb.IsFull() {
		t.Fatalf("expect IsFull is false but got true")
	}

	// write to, isFull
	err = rb.WriteByte('b')
	if err != nil {
		t.Fatalf("WriteByte failed: %v", err)
	}
	if rb.Length() != 2 {

    }
  }

  public void testPut() {
    assertThat(table.put("foo", 1, cellValue('a'))).isNull();
    assertThat(table.put("bar", 1, cellValue('b'))).isNull();
    assertThat(table.put("foo", 3, cellValue('c'))).isNull();
    assertEquals((Character) 'a', table.put("foo", 1, cellValue('d')));
    assertEquals((Character) 'd', table.get("foo", 1));

    assertThat(parse(url, "a\u0000b=cd")).isNull()
    assertThat(parse(url, "ab=c\u0000d")).isNull()
    assertThat(parse(url, "a\u0001b=cd")).isNull()
    assertThat(parse(url, "ab=c\u0001d")).isNull()
    assertThat(parse(url, "a\u0009b=cd")).isNull()
    assertThat(parse(url, "ab=c\u0009d")).isNull()
    assertThat(parse(url, "a\u001fb=cd")).isNull()
    assertThat(parse(url, "ab=c\u001fd")).isNull()

    CompactLinkedHashMap<Integer, String> map = CompactLinkedHashMap.create();
    assertThat(map.needsAllocArrays()).isTrue();
    assertThat(map.entries).isNull();
    assertThat(map.keys).isNull();
    assertThat(map.values).isNull();
    assertThat(map.links).isNull();

    map.put(1, Integer.toString(1));
    assertThat(map.needsAllocArrays()).isFalse();
    assertThat(map.entries).hasLength(CompactHashing.DEFAULT_SIZE);

    assertThat(spec.initialCapacity).isNull();
    assertThat(spec.maximumSize).isNull();
    assertThat(spec.maximumWeight).isNull();
    assertThat(spec.concurrencyLevel).isNull();
    assertThat(spec.keyStrength).isNull();
    assertThat(spec.valueStrength).isNull();
    assertThat(spec.writeExpirationTimeUnit).isNull();
    assertThat(spec.accessExpirationTimeUnit).isNull();

  }

  public void testHigherEntry() {
    assertThat(create().higherEntry("a")).isNull();
  }

  public void testHigherKey() {
    assertThat(create().higherKey("a")).isNull();
  }

  public void testLastEntry() {
    assertThat(create().lastEntry()).isNull();
  }

  public void testLastKey() {
    NavigableMap<String, Integer> map = create();
    map.put("a", 1);

    assertThat(request.body).isNull()
  }

  @Test
  fun userAgent() {
    val request = fromArgs("-A", "foo", "http://example.com").createRequest()
    assertThat(request.method).isEqualTo("GET")
    assertThat(request.url.toString()).isEqualTo("http://example.com/")
    assertThat(request.header("User-Agent")).isEqualTo("foo")
    assertThat(request.body).isNull()
  }

  @Test