Cannot read property 'char_filter' of null

[elmarti]

I'm submitting a...

[ ] Regression (a behavior that used to work and stopped working in a new release)
[x] Bug report  
[ ] Feature request
[ ] Documentation issue or request
[ ] Support request => Please do not submit support request here, instead see https://github.com/LokiJS-Forge/LokiDB/blob/master/CONTRIBUTING.md#question

Current behavior

I'm running LokiDB in electron with the @lokidb/fs-storage adapter and @lokidb/full-text-search.
Everything works fine, apart from when I attempt to run a $fts query, the following is returned:

(node:74814) UnhandledPromiseRejectionWarning: TypeError: Cannot read property 'char_filter' of null
    at analyze (/Users/<USER>/dbClient/node_modules/@lokidb/full-text-search/webpack:/@lokidb/full-text-search/packages/full-text-search/src/analyzer/analyzer.ts:30:16)
    at index_searcher_IndexSearcher._recursive (/Users/<USER>/dbClient/node_modules/@lokidb/full-text-search/webpack:/@lokidb/full-text-search/packages/full-text-search/src/index_searcher.ts:223:23)
    at index_searcher_IndexSearcher.search (/Users/<USER>/dbClient/node_modules/@lokidb/full-text-search/webpack:/@lokidb/full-text-search/packages/full-text-search/src/index_searcher.ts:67:29)
    at full_text_search_FullTextSearch.search (/Users/<USER>/dbClient/node_modules/@lokidb/full-text-search/webpack:/@lokidb/full-text-search/packages/full-text-search/src/full_text_search.ts:89:30)
    at result_set_ResultSet.find (/Users/<USER>/dbClient/node_modules/@lokidb/loki/webpack:/@lokidb/loki/packages/loki/src/result_set.ts:622:56)
    at QueryCacheService._callee3$ (/Users/<USER>/dbClient/src/main/services/query-cache.service.ts:109:33)
    at tryCatch (/Users/<USER>/dbClient/src/node_modules/regenerator-runtime/runtime.js:63:40)
    at Generator.invoke [as _invoke] (/Users/<USER>/dbClient/src/node_modules/regenerator-runtime/runtime.js:294:22)
    at Generator.next (/Users/<USER>/dbClient/src/node_modules/regenerator-runtime/runtime.js:119:21)
    at asyncGeneratorStep (/Users/<USER>/dbClient/src/node_modules/@babel/runtime/helpers/asyncToGenerator.js:3:24)

Expected behavior

FTS query executes without failure.

Minimal reproduction of the problem with instructions

Initialising the database connection

    const dbPath = path.join(app.getPath('userData'), 'db.json');
    console.log({dbPath});
    if(!fs.existsSync(dbPath)){
      fs.writeFileSync(dbPath, '{"collections":{}}', "UTF-8", { flags: 'w+'});
    }

    FSStorage.register();
    LokiFullTextSearch.register();

    this.db = new loki(dbPath, {
      serializationMethod: 'normal',
      env: 'NODEJS',
    });

    await this.db.initializePersistence({
      autosave: false,
      autosaveInterval: 1000,
      autoload: false,
      throttledSaves: false,
      adapter: memAdapter,
    })
    await this.db.saveDatabase();
  }

Running an fts query

 async filter(
    collectionId: any,
    query: {},
    sort: any,
    position: { page: number; offset: number; limit: any },
    columns: Array<any>
  ) {
    console.log({ queryId });
    const collection = this.db.getCollection(collectionId)
    const queryObj = {};
    let queryBuilder = collection.chain();
    if (Object.keys(query).length > 0) {
      for (const key in query) {
        const column = columns.find((x) => x.key === key);
        if (column.type.js === 'datetime' || column.type.js === 'date') {
          //{key: {'$between': [value0, value1]}
          queryObj[key] = {
            '$between': query[key].map((x) => new Date(x))
          }
        } else {
          queryObj['$fts'] = {
            query: {
              type: "match",
              field: key,
              value: query[key][0],
              // prefix_length: 1,
              fuzziness: 0,
              extended: true,
              // minimum_should_match: 1
            }
          }
        }
      }
    }
    console.log('queryObj', queryObj);
    queryBuilder = queryBuilder.find(queryObj);
    if (sort) {
      queryBuilder = queryBuilder.simplesort(sort.key, {desc: sort.order === 'desc'});
    }

    const total = queryBuilder.count();
    queryBuilder = queryBuilder.offset(position.page);
    queryBuilder = queryBuilder.limit(position.limit);
    return {
      _id: queryId,
      result:  queryBuilder.data(),
      pagination: {
        total,
        current: position.page,
        pageSize: position.limit,
      },
    };
  }

Environment

• Electron
• "@types/lokijs": "^1.5.7",
• "@lokidb/fs-storage": "^2.1.0",
• "@lokidb/full-text-search": "^2.1.0",
• "@lokidb/loki": "^2.1.0",