SUM with NULL Values in Teradata

In Teradata, when you SUM a value that is nullable, does it work correctly if there are null values? Here's the test and the result. The answer is yes, it works fine.

CREATE VOLATILE TABLE rgWork1 (
    client      INT         NOT NULL,
    flag        byteint 
) UNIQUE PRIMARY INDEX (client) 
ON COMMIT PRESERVE ROWS;

INSERT INTO rgWork1 (client, flag) VALUES (1, 1); 
INSERT INTO rgWork1 (client, flag) VALUES (2, 0);
INSERT INTO rgWork1 (client, flag) VALUES (3, NULL);

SELECT SUM(flag)
FROM rgWork1;
 
SELECT SUM(flag)
FROM rgWork1 
WHERE flag = 1;
 
SELECT SUM(flag)
FROM rgWork1
WHERE flag IS NOT NULL;
 
SELECT SUM(flag)
FROM rgWork1
WHERE (flag = 1 OR flag IS NOT NULL);

All of these queries return the correct answer of 1.