Fix: indexError for [] candidates

[hemanth]

This PR fixes the indexError but not the root cause.

For cases where candidates are [] we end up with IndexError: list index out of range maybe it is a limitation of bison? Should we show a default error message?

For the below input we always get an indexError:

input:
Can you fetch from URL?

output:

{'messages': [{'author': '0', 'content': 'Can you fetch from URL?'}], 'candidates': []}

[markmcd]

Thanks, and congrats on being the first external PR 👍

LGTM but @MarkDaoust or @shilpakancharla know this part better than me, so I'll wait for them.

[MarkDaoust]

Yes, thanks, for the PR!

This change avoids the index error, but I think its a little too subtle about it.

import this -> "Errors should not pass silently"

After the call anyone who isn't dealing with candidates themselves is expecting that the last item in messages is the response from the model, and .last is the text of that response. If there was no response I'd want to have a None in both those locations.

If we just skip the append like this and you call reply you'll be replying to your previous message, with no message from the bot in between, and because the we assume alternating messages, you'll have switched roles with the bot which is strange. I'd rather just fail with a clear error in reply.

I was actually fixing this in this PR (its kind of a mess but look at chat.py): #7

So I'm sorry I have to close this. But thanks for finding us and helping out, we really appreciate it.

[MarkDaoust]

Please reach out if you find any other issues.

[hemanth]

Thank you! Yes, that makes sense, better than erroring out or silently failing.

 if response["candidates"]:
    last = response["candidates"][0]
 else:
    last = None
 request["messages"].append(last)