'Ensures that the class and tag specified exist as an alternative. This
custom version fixes parsing broken encodings there a V2 attribute
# certificate is encoded as a V1
:param class_:
The integer class_ from the encoded value header
:param tag:
The integer tag from the encoded value header
:param contents:
A byte string of the contents of the value - used when the object
is explicitly tagged
:raises:
ValueError - when value is not a valid alternative'

def validate(self, class_, tag, contents):

    super(CertificateChoices, self).validate(class_, tag, contents)
    if (self._choice == 2):
        if (AttCertVersion.load(Sequence.load(contents)[0].dump()).native == u'v2'):
            self._choice = 3
