vincenttouzet/BootstrapFormBundle — pull request #5 by lazyants (2013-08-31 10:03:50+00:00)
Title: allow_single_deselect for chosen

When a single select box isn't a required field, you can set allow_single_deselect: true and Chosen will add a UI element for option deselection. This will only work if the first option has blank text.

http://harvesthq.github.io/chosen/#allow-deselect-on-single-selects