Conditional "Empty" state clear button (<input type="submit"/>) label.

Problem/Motivation

When the field widget element contains buttons, the conditional "empty" state clears out button labels.

Steps to reproduce

1. Configure a conditional "empty" state for a field.
2. Assign a field widget for the field which contains input buttons.
3. When "empty" state is triggered, it will clear button labels ("value" attribute of input submit button)