Allow empty 'error' to be in repsonse.

[tdivis]

Reason: some servers send 'error': None.

[coveralls]

Coverage remained the same at 100.0% when pulling 6fdcde9 on tdivis:allow-empty-error-field into 124e9f6 on armills:master.

[tdivis]

This was needed to call functions of trac JSON-RPC API.

[emlove]

This should really be fixed on the trac side. Per the JSON-RPC Response specifications, the error key must not exist if there is no error.

Alternatively, we could add hooks for downstream libs to register a callback and massage the data before passing it to parse_response to account for non-conforming servers. I imagine it's easiest to just fix the problem at the source though.

[tdivis]

I'm afraid trac uses JSON-RPC 1.0, where specifications says, "error - An Error object if there was an error invoking the method. It must be null if there was no error.".

This pull request allows jsonrpc-base to work with both JSON-RPC 1.0 and 2.0.

[emlove]

Ah, I see. I that case, my small preference would be call it out explicitly, instead of relying on it being falsey just to be extra safe. (if data.get('error') is not None:) And we'll need to add an extra test for the JSON-RPC 1.0 format to make sure this isn't accidentally refactored in the future.

It should be sufficient to copy the block below, and test with a response that includes "error": None.
https://github.com/armills/jsonrpc-base/blob/124e9f6ad7d0ae62ea903d639bf4db217b50768d/tests.py#L195-L204

[tdivis]

OK, I did that. Also had to fix tox.ini as there was bug (duplicate testenv:py35 entry).

[emlove]

Thanks for the contribution! 🌟

[emlove]

I'll get new versions pushed out later today.