Fix possible error when recursing exceptions
Fix possible error when recursing exceptions

The method "current()" from NestedValidationException can return any
instance of ValidationException, but the implementation of
"getChildren()" requires it to return an instance of
"NestedValidationException".

Signed-off-by: Henrique Moody <3be1622bc44cadc0ae4da5043bd847b230c854e8@gmail.com>

Respect/Validation,Respect/Validation