avoiding inline if (bunq#93)

at the cost of risk for index-out-of-bounds (prior code)

src/main/java/com/bunq/sdk/model/core/UserContextHelper.java

@@ -31,7 +31,7 @@ public User getFirstUser() {
     BunqResponseRaw responseRaw = getRawResponse(USER_URL);
     BunqResponse<List<User>> response = fromJsonList(User.class, responseRaw);
 
-    return !response.getValue().isEmpty()?response.getValue().get(FIRST):null;
+    return response.getValue().get(FIRST);
   }
 
   public MonetaryAccountBank getFirstActiveMonetaryAccountBankByUserId(Integer userId) {