@Test
  public void testIsNullOperation() {
    // Currently, if one predicate in SELECT contains not existed series, we won't show this column.
    // So we test IS_NULL in WHERE.
    String[] expectedHeader =
        new String[] {
          "s1", "_col1", "_col2", "_col3", "_col4",
        };
    String[] retArray =
        new String[] {
          "1,true,false,true,false,", "2,true,false,true,false,", "3,true,false,true,false,",
        };
    tableResultSetEqualTest(
        "select s1,s2 is null, s2 is not null, s5 is null, s5 is not null from sg1",
        expectedHeader,
        retArray,
        DATABASE_NAME);
  }
CompareOperations: =, >, <, like, in, between...(don't include `is null`)

<p>The result will be NULL if any Operand of CompareOperations is NULL.
integration-test/src/test/java/org/apache/iotdb/relational/it/query/old/query/IoTDBNullOperandTableIT.java