null values for queryParameters cause exception

[einverne]

Description

In http_request.dart file, when we use dio to send requests, the queryParameters is null, and cause the exception

DioException [unknown]: null
Error: type 'Null' is not a subtype of type 'Object'

Expected behavior
No exception.

Current behavior
What happened.

Screenshots or Logs

Environment (please complete the following information):

• OS: [e.g. Debian GNU/Linux]
• Meilisearch version: [e.g. v.0.20.0]
• meilisearch-dart version: 0.17.0