Find out if a parameter/return field is NULLABLE using Describe

It doesn't seem to be possible to find out if a parameter or result
field is nullable using the Describe protocol.

For example if I have this table and statement:
 create table employees (   id serial not null primary key,   name text not null,   email text
 <-- this field );
 
 insert into employees (name, email) values ($1, $2);

Then the only information I get back about $2 is that it's a TEXT (OID
= 25), when clearly $1 and $2 are different in that one is nullable
and the other isn't.

Similarly,
 select name, email from employees;

This time I get more information about the types, including a modifier
and length, but I can't see whether that lets me find out that one
could be NULL and the other can never be.

So is this possible?

Rich.

-- 
Richard Jones, CTO Merjis Ltd.
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