postgres boolean function and check constraint

Question

I been using postgres for a while. Mostly simple stuff.

Now trying to implement a small perl function to check for a single valid email address.

My employees table should have either a single valid email address, or none (ie empty, zilch). I assume none means undef(email)

My sample code below.

I'm trying to return FALSE only if the given variable is NOT an email address.

The function appears to correctly check a given email address, BUT wrongly returns FALSE if email is blank or empty.

Grateful for any help to show me how to do this the-right-way.

CREATE OR REPLACE FUNCTION email_valid(email text) RETURNS boolean AS
$BODY$
use Email::Address;
my $answer = 1;
return $answer if (undef ($_[0]));
my @address = Email::Address->parse($_[0]);
$answer = scalar(@address);
return $answer;
$BODY$
LANGUAGE plperlu;

ALTER TABLE employees
ADD CONSTRAINT check_email CHECK (email_valid(email) = TRUE) ;

Edit. Here's the revised procedure commented below, in easier to read format. :-)

CREATE OR REPLACE FUNCTION public.email_valid(email text) RETURNS boolean AS $BODY$ use Email::Address; my $input = shift; return('TRUE') if ($input eq ''); my @address = Email::Address->parse($input); return (@address == 1 ? 'TRUE' : 'FALSE'); $BODY$ LANGUAGE plperlu

This is a different question to the similar previous question at What is the best way to store an email address in PostgreSQL?

I need to also allow null or blank email address, whereas other question and answer will require valid e-address.