Syntax issue?

When introducing a new string to a formula we ended up dropping income values of certain transactions. The new string's purpose is to eliminate transactions double posting due to a script that runs on our invoices.

I need help to identify if the second set of formula are written incorrectly, or if any glaring issues appear to anyone.

The original formulae:
to_char({debitamount},'9999999.99')
and:
to_char(({creditamount}*-1),'9999999.99')

The revisions:
CASE WHEN ({account.custrecord_house_account} = 'T' AND {debitamount} IS NOT NULL) THEN '0.00' ELSE to_char({debitamount},'9999999.99') END
and:
CASE WHEN ({account.custrecord_house_account} = 'T' AND {creditamount} is not null) THEN '0.00' ELSE to_char(({creditamount}*-1),'9999999.99') END