COPY error with null date

Using 8.3.3 I am trying to import a CSV file using the following copy
command.

copy billing.contact from 'c:/export/contact.csv'
with delimiter as ','
null as ''
csv quote as '"';

The following record record causes an error because the third field, "",
is a null date and causes the error following the record. How can I
change the copy command above so that a null date or number will be
imported as null? I do not care if empty strings are imported as an
empty string or a null.

Bill

"IASAcctSys","09/09/1995","",...


ERROR:  invalid input syntax for type date: ""
CONTEXT:  COPY contact, line 6, column date: ""

********** Error **********

ERROR: invalid input syntax for type date: ""
SQL state: 22007
Context: COPY contact, line 6, column date: ""