No items under pallet returns an error

[Imod7]

Description
If no items are found under a Pallet this is not necessarily an error.

Example
When connected to Kusama, the request /pallets/ParaSessionInfo/errors?at=29205809 returns:

{
  "code": 400,
  "message": "no queryable errors items found for palletId \"paraSessionInfo\"",
  "stack": "BadRequestError: no queryable errors items found for palletId \"paraSessionInfo\"\n    at PalletsErrorsService.....
  "level": "error"
}

Other examples with Pallets are the following: ParachainsOrigin, Parameters.

Suggestion
Return an empty array of items instead.