Why is my JSONObject related unit test failing?

I'm running my tests using gradle testFlavorType

JSONObject jsonObject1 = new JSONObject();
JSONObject jsonObject2 = new JSONObject();
jsonObject1.put("test", "test");
jsonObject2.put("test", "test");
assertEquals(jsonObject1.get("test"), jsonObject2.get("test"));

The above test succeeds.

jsonObject = new SlackMessageRequest(channel, message).buildBody();
String channelAssertion = jsonObject.getString(SlackMessageRequest.JSON_KEY_CHANNEL);
String messageAssertion = jsonObject.getString(SlackMessageRequest.JSON_KEY_TEXT);
assertSame(channel, channelAssertion);
assertSame(message, messageAssertion);

But the above two requests fail. The stack trace says that channelAssertion and messageAssertion are null, but not sure why. My question is: Why are the above two asserts failing?

Below is the SlackMessageRequest.

public class SlackMessageRequest
        extends BaseRequest {
    // region Variables

    public static final String JSON_KEY_TEXT = "text";
    public static final String JSON_KEY_CHANNEL = "channel";

    private String mChannel;
    private String mMessage;

    // endregion

    // region Constructors

    public SlackMessageRequest(String channel, String message) {
        mChannel = channel;
        mMessage = message;
    }

    // endregion

    // region Methods

    @Override
    public MethodType getMethodType() {
        return MethodType.POST;
    }    

    @Override
    public JSONObject buildBody() throws JSONException {
        JSONObject body = new JSONObject();
        body.put(JSON_KEY_TEXT, getMessage());
        body.put(JSON_KEY_CHANNEL, getChannel());
        return body;
    }

    @Override
    public String getUrl() {
        return "http://localhost:1337";
    }

    public String getMessage() {
        return mMessage;
    }

    public String getChannel() {
        return mChannel;
    }

// endregion
}