@Test
public void isNullNode() {

    NullNode node = NullNode.nullNode();
    assertEquals(false, node.isObjectNode());
    assertEquals(false, node.isArrayNode());
    assertEquals(false, node.isStringNode());
    assertEquals(false, node.isNumberNode());
    assertEquals(false, node.isBooleanNode());
    assertEquals(true, node.isNullNode());
}