'Get an rdataset matching the specified properties in the
current node.
None is returned if an rdataset of the specified type and
class does not exist and I{create} is not True.
@param rdclass: The class of the rdataset
@type rdclass: int
@param rdtype: The type of the rdataset
@type rdtype: int
@param covers: The covered type.
@type covers: int
@param create: If True, create the rdataset if it is not found.
@type create: bool
@rtype: dns.rdataset.Rdataset object or None'

def get_rdataset(self, rdclass, rdtype, covers=dns.rdatatype.NONE, create=False):

    try:
        rds = self.find_rdataset(rdclass, rdtype, covers, create)
    except KeyError:
        rds = None
    return rds
