On: A liar who always lies says "All my hats are green...

[lukas099]

Is there not a convention within formal logic defining this type of statement to be true or false?

[gabrielhidasy → lukas099]

There is, it's the "Vacuous Truth", generally any affirmation about elements of the empty set is true. It's very useful as it allows you to convert any statement "All elements of x are Y" in "No element in x is Not Y".

[scotty79 → lukas099]

There is.

  [].all(x => whatever(x)) == true

At least that's how math usually thinks about it.