Github user zjffdu commented on the issue:
https://github.com/apache/zeppelin/pull/2272
@jongyoul Thanks for the review. Copy my comment above.
```
toJson and fromJson is used in both zeppelin-interpreter and
zeppelin-zengine. I didn't find a proper place to put the common interface. And
actually the interface doesn't eliminate the code duplication, the sub classes
still need to implement toJson as not every classes share the same Gson (some
class need custom Gson). So I didn't add a common interface.
```
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