# documentRepository method Null safety

1. @override

DocumentRepository? documentRepository(

1. String? appId

)
override

## Implementation

    @override
    DocumentRepository? documentRepository(String? appId) {
      if ((appId != null) && (_documentRepository[appId] == null)) {
        _documentRepository[appId] = DocumentCache(DocumentFirestore(
            () => appRepository()!.getSubCollection(appId, 'document'), appId));
      }
      return _documentRepository[appId];
    }