@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[] {
          TIMESTAMP_STR,
          "root.test.sg1.s1",
          "root.test.sg1.s2 IS NULL",
          "root.test.sg1.s2 IS NOT NULL",
          "root.test.sg1.s5 IS NULL",
          "root.test.sg1.s5 IS NOT NULL",
        };
    String[] retArray =
        new String[] {
          "1,1,true,false,true,false,", "2,2,true,false,true,false,", "3,3,true,false,true,false,",
        };
    resultSetEqualTest(
        "select s1,s2 is null, s2 is not null, s5 is null, s5 is not null from root.test.sg1",
        expectedHeader,
        retArray);
  }
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/db/it/query/IoTDBNullOperandIT.java