'Partially serialize.
Following the example, **partial serialization** means the following::
assert isinstance(Bar().to_partial_json()[0], Foo)
assert isinstance(Bar().to_partial_json()[1], Foo)
# in particular...
assert Bar().to_partial_json() != [\'foo\', \'foo\']
:raises acme.jose.errors.SerializationError:
in case of any serialization error.
:returns: Partially serializable object.'

@abc.abstractmethod
def to_partial_json(self):

    raise NotImplementedError()
