Tip for your 'null' problem: LLMs are set up to output tokens. Not to not output tokens. So instead of "don't return anything" have the lack of results "retur

Tip for your 'null' problem: LLMs are set up to output tokens. Not to not output tokens. So instead of "don't return anything" have the lack of results "return the default value of XYZ" and then just do a text search on the result for that default value (i.e. XYZ) the same way you do the text search for the state names. Also, system prompts can be very useful. It's basically your opportunity to have the LLM roleplay as X. I wish they'd let the system prompt be passed directly, but it's still better than nothing.