add comment on Option<()> to answer FAQ

runtime/parachains/src/initializer.rs

@@ -34,7 +34,13 @@ pub trait Trait: system::Trait + configuration::Trait + paras::Trait { }
 decl_storage! {
 	trait Store for Module<T: Trait> as Initializer {
 		/// Whether the parachains modules have been initialized within this block.
-		/// Should never hit the trie.
+		///
+		/// Semantically a bool, but this guarantees it should never hit the trie,
+		/// as this is cleared in `on_finalize` and Frame optimizes `None` values to be empty values.
+		///
+		/// As a bool, `set(false)` and `remove()` both lead to the next `get()` being false, but one of
+		/// them writes to the trie and one does not. This confusion makes `Option<()>` more suitable for
+		/// the semantics of this variable.
 		HasInitialized: Option<()>;
 	}
 }