Problem: empty topics in rpc response is not tested

[yihuang]

backport: #254

Solution:

• merge empty topics fix
• add integration tests to verify

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Thank you for your code, it's appreciated! :)

[thomas-nguy]

we can probably also add the ante handler fix at the same time

[yihuang]

that one should be fixed privately first I think.

[leejw51crypto]

lgtm