main.dart

import 'dart:convert';

void main() {
  var org = <String, dynamic>{
    'id': '12345678990',
    'name': 'Roga & Kopyta',
    'facebook': null
  };
  print(toCypherObject(org));
}

String toCypherObject(Map<String, dynamic> obj) {
  final obj_ = Map.from(obj)..removeWhere((key, value) => value == null);
  final encoded = obj_.entries.fold<List<String>>(
      [],
      (encodedEntries, entry) => encodedEntries
        ..add('${entry.key}: ${json.encode(entry.value)}')).join(', ');
  return '{$encoded}';
}