Concatenation containing a "null" term

(I am certain I once saw the answer to the following question, but I can't
for the life of me find out where!)

I create a View as

SELECT (firstname || ' ' || lastname)::character(50) AS fullname
FROM name_table;

firstname and lastname are text columns, and firstname may be null.

Unfortunately, it seems that whenever firstname is null, the resulting
fullname is null also. Is there a way of having the null-strings terms of
the concatenation operator be considered as empty strings instead?

Thanks for the help!