build method
Builds the query
Implementation
Map<String, dynamic> build() {
return {
if (_filter.isNotEmpty) 'filter': _filter,
if (_sort.isNotEmpty) 'sort': _sort,
if (_limit != null) 'limit': _limit,
if (_skip != null) 'skip': _skip,
if (_fields != null) 'fields': _fields,
};
}