| Q             | A
| ------------- | ---
| Branch?       | 4.3
| Tickets       | refs #7966
| License       | MIT
| Doc PR        | ∅

FieldsBuilder called filterLocator->has() with whatever QueryParameter::$filter
returned, crashing on object-form filters (new SortFilter()) when the parameter
key contained '['. A resolveFilter() helper now handles both string service ids
and FilterInterface instances, applied at every locator site.