Fixed a bug on PagePermissions

@@ -70,7 +70,7 @@ class PagePermissions {
         }
 
         // Meta value hasn't been set, getting settings defaults
-        if ('' === $data = array_shift(get_post_meta($post_id, self::META))) {
+        if (NULL === $data = array_shift(get_post_meta($post_id, self::META))) {
             $data = Array(self::ELE_SEL => $settings[self::ELE_SEL], self::ELE_CUST => $settings[self::ELE_CUST]);
         }
 
@@ -204,7 +204,7 @@ class PagePermissionsAdmin {
         $selected = ($post->ID == 0 ? self::getOptions() : array_shift(get_post_meta($post->ID, PagePermissions::META)));
 
         // If the post doesn't have the field saved get defaults
-        if (empty($selected)) {
+        if (is_null($selected)) {
             $selected = self::getOptions();
         }
 
@@ -277,7 +277,7 @@ class PagePermissions_Actions {
                 $new[PagePermissions::ELE_CUST] = Array();
             }
     
-            if (empty($current)) {
+            if (is_null($current)) {
                 add_post_meta($real_id, PagePermissions::META, $new, true);
             } else {
                 update_post_meta($real_id, PagePermissions::META, $new);
@@ -296,7 +296,7 @@ class PagePermissions_Actions {
         $innerhtml = '';
         if ('0' !== ($change_field = (isset($_GET['attachment_id']) ? 'attachments[' . $_GET['attachment_id'] . '][' . PagePermissions::META . ']' : '0'))) {
             $selected = array_shift(get_post_meta($_GET['attachment_id'], PagePermissions::META));
-            if (empty($selected)) {
+            if (is_null($selected)) {
                 $selected = PagePermissionsAdmin::getOptions();
             }
 
@@ -333,7 +333,7 @@ class PagePermissions_Actions {
             $new[PagePermissions::ELE_CUST] = Array();
         }
 
-        if (empty($current)) {
+        if (is_null($current)) {
             add_post_meta($real_id, PagePermissions::META, $new, true);
         } else {
             update_post_meta($real_id, PagePermissions::META, $new);