HttpClient NPE bug when add queryparam

[symphony-hong]

Bug Report

When we try to add a query param to a HttpClient instance, a NPE will be thrown because the queryParams in RequestConfig was initialised with null and same for headers, cookies and formParams.
Ref

Steps to Reproduce:

Reproduce with the unittest:

final HttpClient httpClient = HttpClient.builder(this::mockedApiClientBuilder)
      .basePath("https://localhost:8080")
      .header("Connection", "Keep-Alive")
      .header("Keep-Alive", "timeout=5, max=1000")
      .cookie("foo", "bar")
      .build();

httpClient.queryParam("test", "test");

Expected Result:

The query param is added successfully.
Same for headers, cookies, formParams

Actual Result:

java.lang.NullPointerException
	at com.symphony.bdk.http.api.HttpClient$RequestConfig.appendQueryParam(HttpClient.java:394)
	at com.symphony.bdk.http.api.HttpClient.queryParam(HttpClient.java:182)
	at com.symphony.bdk.http.api.HttpClientTest.usage(HttpClientTest.java:22)

Environment:

symphony-bdk-2.1.0

[thibauult]

@symphony-hong PR created #463

[thibauult]

Release 2.1.1 should be available soon in Maven Central.

[symphony-youri]

Do we need to merge into master too?

[thibauult]

Already backported onto main : 723a4a7