[Form] allowed an empty value to be displayed for choices even when required is true
[Form] allowed an empty value to be displayed for choices even when required is true

Rules are as follows:

* If multiple is true, then the empty_value is ignored
* If not, and if the field is not required, the empty_value is set to the empty string by default and displayed
* If the field is required, and if the user explicitely set the empty_value, then it is displayed

symfony/framework-bundle