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).
Third-party code that is *not* part of the application image (the Google App
Engine SDK in trunk/thirdparty/google_appengine, for example) belongs in
trunk/thirdparty. For third-party code that *is* part of the application
image, see the notes in trunk/app/README.
== THIRD PARTY LICENSES ==
Third-party code must also include a license text file, named LICENSE or
COPYING, in the package subdirectory. If the third-party package subdirectory
is maintained automatically with a tool such as svn_load_dirs.pl (which
removes files, such as license text files, that were added later to the
"target" directory), place the license text file in the trunk/app directory
and add the package name as a suffix.