I created table with, ID(integr), timestamps, date, time data types in fields.
I added data into it adding NULL into some fields, it inserted default data into these fields, other fields remains empty.

SELECT CAST( "timestamp" AS DATE ) FROM "Table"
SELECT CAST( "date" AS DATE ) AS "one" FROM "Table"

When these queries run instead of empty fields I get, 1-01-02 date value instead of empty field.

Similar happens with 
SELECT CAST( "timestamp" AS TIME ) FROM "Table"
SELECT CAST( "time" AS TIME ) FROM "Table"

When these queries run instead of empty fields I get, 00:00:00 time value instead of empty field.

If I run hsqldb server and run same queries in database manager I get empty fields when no data in table.

This happens same in DEV300m101, OOo 3.3 and cws dba34d from qa-upload.