Select element required validation

[dpinheiro]

When using a choice element, rendered by a select element, if the empty_value is not null and the required is set to true, the validation still pass even if no option is selected. This issue is occurring at least on Chrome 33.0.1750.152 @ Linux.

Looking at the source code, I guess the problem is that no empty value is associated to the option of the empty_value. Adding value="" after option in the line 197 of file bootstrap.html.twig solved my problem.