message: added filter validation for filters that are purely searching by card type
diff: @@ -2,6 +2,7 @@ import { CardId } from '@cardstack/core/card';
  import * as JSON from 'json-typescript';
  import { CARDSTACK_PUBLIC_REALM } from '@cardstack/core/realm';
  import CardstackError from '@cardstack/core/error';
  +import isEqual from 'lodash/isEqual';
  import { assertJSONValue, assertJSONPrimitive } from './json-validation';
  export interface Query {
  @@ -129,6 +130,9 @@ export function assertFilter(filter: any, pointer: string[]): asserts filter is
  if ('type' in filter) {
  assertCardId(filter.type, pointer.concat('type'));
  + if (isEqual(Object.keys(filter), ['type'])) {
  + return; // This is a pure card type filter
  + }
  }
  if ('any' in filter) {
  