concat string and null

Hello Team,

can you please advise how to replace nulls by a default value?

select concat(cast(glb.budget_version_id as string)," ", cast(glc.segment1 as string)) as balid
from oracle_financial.gl_balances glb,
oracle_financial.gl_code_combinations glc,
oracle_financial.gl_ledgers glg ;

If I add a null to a value, null will be returned.

I tried NVL it is not working.

Thanks,

Roshan