v3.0.0

Features

• Serialize the empty string to undefined (#22) (8a89294), closes #20

BREAKING CHANGES

• Serialization of the empty string is now treated as undefined instead of an UnserializableParamError.

Otherwise, the serialization of { foo: null } would conflict with { foo: '' }.
This serializer chooses to support the more common and more useful case of sending null
as a meaningful value while treating the empty string as sending no value.
This aligns with common UX patterns where input fields are initialized to the empty string.