Feed email undefined error

From Joomla! Documentation

undefined error

When upgrading from an earlier version, you might encounter "Undefined Variable: feed_email" warnings when viewing feeds or Global Config admin screen. This is because a NEW FEATURE was added to Joomla 1.5.10 and a new configuration var was added. To fix this, just edit and then resave your Global Configuration using the administrator console. This adds the $feed_email var to your /configuration.php file.