In 4.3, EmailValidator was updated to pass the value through IDN.toAscii before applying the regular expression. The Javadocs for IDN.toAscii document a set of cases which can result in an IllegalArgumentException being thrown, but EmailValidator does not attempt to catch that exception. As a result, in certain circumstances, rather than returning false the validator throws an exception. That, in turn, results in this:
This situation was not possible in 4.2.