Some said in old sql standard, zero-length (empty) string will be converted to
null, eg,
update foo set bar=''
will effectively become
update foo set bar=null

Is this true for FB1.5 and FB2 ?

A related question, in DDL, is
a varchar(10) default ''
equivalent to
bar varchar(10) default null

(For your information MS Access does allow zero-length string)

regards,
bill