Missing argument 1 for PictureMapping::export()

Problem/Motivation

Using the latest dev release, I updated the feature which included picuture and breakpoint settings. Reverting the feature resulted in:

Missing argument 1 for PictureMapping::export(), called in                                                                             [warning]
/.../sites/all/modules/contrib/features/features.export.inc on line 564 and
defined PictureMapping.php:357
... 6 times repeated ...

The feature diff included:

--- a/.../example.default_picture_mapping.inc
+++ b/.../example.default_picture_mapping.inc
@@ -21,16 +21,12 @@ function example_default_picture_mapping() {
       '1x' => array(
         'mapping_type' => 'image_style',
         'image_style' => 'contentimage_bp_smartphone',
-        'sizes' => '',
-        'sizes_image_styles' => array(),
       ),
     ),
     'breakpoints.theme.anna_y2014.tablet' => array(
       '1x' => array(
         'mapping_type' => 'image_style',
         'image_style' => 'contentimage_breakpoint_tablet',
-        'sizes' => '',
-        'sizes_image_styles' => array(),
       ),
     ),
   );
@@ -47,8 +43,6 @@ function example_default_picture_mapping() {
       '1x' => array(
         'mapping_type' => 'image_style',
         'image_style' => 'headerimage_bp_tablet_1x',
-        'sizes' => '',
-        'sizes_image_styles' => array(),
       ),
     ),
   );