Index: link-template.php
===================================================================
--- link-template.php	(revision 37176)
+++ link-template.php	(working copy)
@@ -190,7 +190,10 @@
 			// having to assign it explicitly
 			if ( empty($category) ) {
 				$default_category = get_term( get_option( 'default_category' ), 'category' );
-				$category = is_wp_error( $default_category ) ? '' : $default_category->slug;
+				if ( isset($category) && ! is_wp_error( $default_category ))
+					$category = $default_category->slug;
+				else 
+					$category = '';
 			}
 		}