String concatenating with Interbase

I have a problem with string concatenating in Interbase. With the synrax

"SELECT FNAME || LNAME AS NAME" the NAME will get a null value when
either FNAME or LNAME is null. This is according to standard T-SQL, but
in Sybase and MSSQL you can write "SELECT ISNULL(FNAME," ") + LNAME AS
NAME" and the query will exchange a blank whenever it encounters a FNAME
with a null value.
(The + is the same as || in Interbase).

Is there any way to do this in Interbase?

Thanks in advance.