def dumpItem(self, item, stream, contentType=None, version=None):
raise NotImplementedError()<EOL>
Converts the specified `item` to serialized form (such that it can
transported over the wire) and writes it to the provided file-like
`stream` object. For agents that support multiple content-types,
the desired `contentType` and `version` will be specified as a
parameter. If `contentType` and `version` are None, appropriate
default values should be used. For agents that concurrently use
multiple content-types, the return value may be a two-element
tuple of (contentType, version), thus overriding or enhancing the
provided values.