Notice: Undefined offset: 0 in tweetbutton_field_formatter_view() message

When adding Tweet Button to a field, the node page displays the following message:

Notice: Undefined offset: 0 in tweetbutton_field_formatter_view() (line 153 of /home/sites/all/modules/tweetbutton/tweetbutton.module).
Notice: Undefined offset: 0 in tweetbutton_field_formatter_view() (line 154 of /home/sites/all/modules/tweetbutton/tweetbutton.module).

Futher, The tweet button does not display at all