This change makes TypeReference usage a little bit easier
- Marking it abstract make it so that usages cannot "forget" subclassing (or omitting the { } part). Previously the error message would be confusing as the supertype would be Object.
- Removing the instanceof check and relying on exception since instantiating TypeReference without a type parameter (new TypeReference() ) *is* exceptional as it goes against the intention of this class altogether.
- Added some clarification to the javadoc regarding intended usage, and a link to prior art for further reading.
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