message: feat(search-backend-module-pg): improve error handling
diff: */
  import { PluginDatabaseManager } from '@backstage/backend-common';
  import { SearchEngine } from '@backstage/plugin-search-backend-node';
  +import { MissingIndexError } from '@backstage/plugin-search-backend-node';
  import {
  SearchQuery,
  IndexableResultSet,
  @@ -92,6 +93,12 @@ export class PgSearchEngine implements SearchEngine {
  this.databaseStore.query(tx, pgQuery),
  );
  + if (!rows.length) {
  + throw new MissingIndexError(
  + `Missing index for ${pgQuery.types}. This means there are no documents to search through.`,
  + );
  + }
  +
  // We requested one result more than the page size to know whether there is
  // another page.
  const { page } = decodePageCursor(query.pageCursor);
  