Create a new approval for the current user to access this hunt.

def CreateApproval(self,
                     reason=None,
                     notified_users=None,
                     email_cc_addresses=None):
    """Create a new approval for the current user to access this hunt."""

    if not reason:
      raise ValueError("reason can't be empty")

    if not notified_users:
      raise ValueError("notified_users list can't be empty.")

    approval = user_pb2.ApiHuntApproval(
        reason=reason,
        notified_users=notified_users,
        email_cc_addresses=email_cc_addresses or [])
    args = user_pb2.ApiCreateHuntApprovalArgs(
        hunt_id=self.hunt_id, approval=approval)

    data = self._context.SendRequest("CreateHuntApproval", args)
    return HuntApproval(
        data=data, username=self._context.username, context=self._context)