}
	// 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 {

		copy(buf[c1:], r.buf[0:c2])
	}

	return buf
}

// IsFull returns this ringbuffer is full.
func (r *RingBuffer) IsFull() bool {
	r.mu.Lock()
	defer r.mu.Unlock()

	return r.isFull
}

// IsEmpty returns this ringbuffer is empty.
func (r *RingBuffer) IsEmpty() bool {
	r.mu.Lock()
	defer r.mu.Unlock()

	return !r.isFull && r.w == r.r
}

    // True if getValue never returns null.
    private boolean isFull() {
      return size == keyToIndex().size();
    }

    K getKey(int index) {
      return keyToIndex().keySet().asList().get(index);
    }

    abstract @Nullable V getValue(int keyIndex);

    @Override
    ImmutableSet<K> createKeySet() {
      return isFull() ? keyToIndex().keySet() : super.createKeySet();
    }

    // True if getValue never returns null.
    private boolean isFull() {
      return size == keyToIndex().size();
    }

    K getKey(int index) {
      return keyToIndex().keySet().asList().get(index);
    }

    abstract @Nullable V getValue(int keyIndex);

    @Override
    ImmutableSet<K> createKeySet() {
      return isFull() ? keyToIndex().keySet() : super.createKeySet();
    }

   *
   * <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();
  }

    }
  }

  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);