Null select

I am performing the select statement which includes formatting a credit card number with "-". However, the problem is if the record returns a null the "-" the statement still returns "---" is there a better way to perform this?

select crcname,
crcexp,
rpad(substr(crcardno,1,4) || '-' || substr(crcardno,5,4) || '-' || substr(crcardno,9,4) || '-' || substr(crcardno,13,4),25,' ') from crcard Received on Fri May 12 2000 - 00:00:00 CDT