Null Value Stored for Date e TimeStamp

Hi,

I would like know about the value stored for null value for fields date 
and timestamp.

Sample             SQL Server 1753/01/01              Oracle         0001/01/01             Informix       1899/01/01
Visual Foxpro  DBF   1899/12/30

I used a tool for migrate database and informed the nullvalues for date 
fields in source and destine database.

I 'm convert DBF to PostgreSQL and the values for null dates from DBF 
are stored as 1899/12/30 in PostgreSQL tables.

Thanks

Fernando Ferreira