How to query all records, when some inputs could be empty

I have a search form:

I want to search for all hunts meeting the forms criteria, which I'm doing successfully when I require all the fields in the form. See conditionals.

My question:

How do I query based on this form, if say, 'category' is not filled in? Meaning the user wants to query all hunts in TX, without caring about the category of the hunt.

Or if they include State, but no Category (all hunts in TX, without caring about category)

Or if they don't include Category or State (all hunts > than now)

We can keep things simple and just use these 3 variables for anyone who wants to help: Start > now (required), State (not required), Category (Not required)

Thanks for any help guys! My app is 95% done!