How to deal with NULL values on dynamic queries?

Hi,

I have a query that some values could be NULL, how can I deal with this
problem?

[code]
EXECUTE 'INSERT INTO '
|| quote_ident(pNOME_VIEW)
|| '('
|| quote_ident(pCHAVE_1)
|| ', DAT_INICIO, DAT_FIM, COMENT) values ('
|| quote_literal(pVAL_CHAVE_1)
|| ', '
|| quote_literal(pVAL_CHAVE_2)
|| ', '
|| quote_literal(pVAL_CAMPO1)
|| ', '
|| quote_literal(pVAL_COMENT)
|| ')';
[/code]

The variable pVAL_COMENT could be NULL or have a value. How can I deal with
this?

Sorry the bad english.

Best Regards,