I am running Apache witha redirect rule like this:
RewriteCond %{HTTP_HOST} ^1st-domain\\.com RewriteRule ^(.*)$ http://2nd-domain.com$1 [R=permanent,L]
I am using the following to catch empty REQUEST_URL:
RewriteEngine on
RewriteCond %{REQUEST_URI} "^/$"
RewriteRule ^(.*) http://%{HTTP_HOST}/my/another/url