Fix 500 when saving /site/edit without email
When saving /site/edit with no no_reply_email set, a 500 error page
would be returned due to an empty value being passed as value to
the datastore (which is not allowed for email fields).
<html>
<head><title>Seed DB links</title></head>
<body>
<p>
<a href="../../seed_db">Seed DB</a> <br />
<a href="../../clear_db">Clear DB</a> <br />
<a href="../../reseed_db">Reseed DB</a> <br />
</p>
<p>
<a href="../../seed_many?start=0&step=15&seed_type=user&end=15&goal=200">
200 Users</a> <br />
</p>
<p>
<a href="../../seed_many?start=0&step=15&seed_type=org&end=15&goal=200">
200 Organizations</a> <br />
<a href="../../seed_many?start=0&step=15&seed_type=org_app&end=15&goal=200">
200 Organizations Pre-Accepted Applications</a> <br />
<a href="../../seed_many?start=200&step=15&seed_type=org_app&end=215&goal=400&status=pre-rejected">
200 Organizations Pre-Rejected Applications</a> <br />
</p>
<p>
<a href="../../seed_many?start=0&step=15&seed_type=mentor&end=15&goal=200">
200 Mentors</a> <br />
</p>
<p>
<a href="../../seed_many?start=0&step=15&seed_type=student&end=15&goal=200">
200 Students</a> <br />
</p>
<p>
<a href="../../seed_many?start=0&step=5&seed_type=student_proposal&end=5&goal=25">
25*rand Student Proposals</a> <br />
</p>
</body>
</html>