public boolean isEmpty() {
    return size == 0;
  }
@Test
  public void testIsEmpty() throws KettleValueException {
    LongHashIndex index = new LongHashIndex();
    assertThat( "Empty index should return true.", index.isEmpty(), is( true ) );
    index.put( 1L, 1L );
    assertThat( "Not empty index should return false.", index.isEmpty(), is( false ) );
  }