to_char() dumps core

In 7.0.2

select to_char(sum(n),'999') from t1;

causes backend dump a core if n is a float/numeric ...data type AND if
sum(n) returns NULL. This seems due to a bad null pointer handling for
aruguments of pass-by-reference data types. I think just a simple
null pointer checking at very top of each function (for example
float4_to_char()) would solve the problem. Comments?

test=# create table t1(f float);
CREATE
test=# select to_char(sum(f),'999') from t1;
pqReadData() -- backend closed the channel unexpectedly.
This probably means the backend terminated abnormally
before or while processing the request.
The connection to the server was lost. Attempting reset: Failed.