Bael-3395: Spring optional path variables (#8106)

* initial test cases

* changes in @requestMapping

spring-mvc-java/src/main/java/com/baeldung/model/Article.java

@@ -0,0 +1,22 @@
+package com.baeldung.model;
+
+public class Article {
+
+    public static final Article DEFAULT_ARTICLE = new Article(12);
+
+    private Integer id;
+
+    public Article(Integer articleId) {
+        this.id = articleId;
+    }
+
+    public Integer getId() {
+        return id;
+    }
+    
+    @Override
+    public String toString() {
+        return "Article [id=" + id + "]";
+    }
+
+}