Add handling for no API key

[ritvik-thesys]

The current implementation just gives a 500 error, with no indication that the key is not set. Maybe we can add a popup in the UI so that if the user forgets to export the key, they can get a proper message for that

[mathcodes]

I can tackle this, but I'm getting a 400 error when submitting a chat. Is that what you are referring to?

[mathcodes]

Never mind, my apologies. That was my code generating the 400. Assign me if you'd like me to tackle this... will also submit PR