Notices shown after upgrade - Undefined index: default in superfish_styles

I have upgraded superfish from 1.8 to 1.9-beta4 and getting the following notices:

  Notice: Undefined index: default in superfish_styles() (line 729 of /domain_path/sites/all/modules/superfish/superfish.module).
    Notice: Trying to get property of non-object in superfish_styles() (line 729 of /domain_path/sites/all/modules/superfish/superfish.module).

I wonder how to resolve this. Please advise. Thanks!