make reputation commitment an OptionQuery

[brenzi]

pallets/reputation-commitments/src/lib.rs

Lines 198 to 199 in 7be60a1

	Option<H256>,
	ValueQuery,

It is bad practise to combine an Option<_> with Value Query, because that makes it less intuitive to evaluate

• if the storage exists (need to check if key exists, querying storage will default to None in two different cases: the storage has never been written, or None has actually been written