payloadFromResponse() will return null if callBack type == Void because GsonConverter cannot work with Void type directly and throws JsonIOException (#119)

Co-authored-by: serhii.kobeza <[email protected]>

Author: SerhiiKobezaCapgemini

guardian/src/main/java/com/auth0/android/guardian/sdk/networking/Request.java

@@ -175,6 +175,7 @@ private Call buildCall() {
     private T payloadFromResponse(Response response) throws GuardianException {
         try {
             final Reader reader = response.body().charStream();
+            if (typeOfT == Void.class) return null;
             return converter.parse(typeOfT, reader);
         } catch (Exception e) {
             throw new GuardianException("Error parsing server response", e);