Fix gcc 9 unused parameter error

[ikbuibui]

Fix for the failing full CI run

[PrometheusPi]

looks okay
but do we need to add [[maybe_unused]] to line 62 too?

[ikbuibui]

[[maybe_unused]] suppresses warnings about variables that might not be used in the current scope. This old compiler sees that the superCellIndex and eFieldBox are not used in the else branch of the if constexpr, so it throws a warning/error, even though they are conditionally used in the if branch on line 62.
[[maybe_unused]] isnt required on line 62 because it isnt defining any parameters which are later not used. It is only returning the cache. It is the responsibility of the caller of this function to store this cache and then use it. If the caller assigns the returned cache to a variable and then doesn't use it this warning/error will be thrown at the caller side.
Just for information, kind of similarly if you want to make sure that the return value of a function is stored (and not ignored/discarded) by the caller, you can declare the function [[nodiscard]].

[PrometheusPi]

@ikbuibui Thanks for the clarification. Thant makes sense, I was following the documentation example here and was a bit confused.

[psychocoderHPC]

Thanks @ikbuibui I planed to fix it too, good that I checked the PRs first