Index: wp-includes/option.php
===================================================================
--- wp-includes/option.php	(revision 28005)
+++ wp-includes/option.php	(working copy)
@@ -967,7 +967,7 @@
 			$row = $wpdb->get_row( $wpdb->prepare("SELECT meta_value FROM $wpdb->sitemeta WHERE meta_key = %s AND site_id = %d", $option, $wpdb->siteid ) );
 
 			// Has to be get_row instead of get_var because of funkiness with 0, false, null values
-			if ( is_object( $row ) ) {
+			if ( is_object( $row ) && $row->meta_value !== '' ) {
 				$value = $row->meta_value;
 				$value = maybe_unserialize( $value );
 				wp_cache_set( $cache_key, $value, 'site-options' );