diff --git a/null-object/etc/test.png b/null-object/etc/test.png
index a29c0a617..bb08b0646 100644
Binary files a/null-object/etc/test.png and b/null-object/etc/test.png differ
diff --git a/null-object/etc/test.ucls b/null-object/etc/test.ucls
index 569663338..79fbc6e92 100644
--- a/null-object/etc/test.ucls
+++ b/null-object/etc/test.ucls
@@ -1,61 +1,69 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<class-diagram version="1.1.8" icons="true" automaticImage="PNG" always-add-relationships="false" generalizations="true" 
-  realizations="true" associations="true" dependencies="false" nesting-relationships="true">  
-  <interface id="1" language="java" name="com.iluwatar.Node" project="null-object" 
-    file="/null-object/src/main/java/com/iluwatar/Node.java" binary="false" corner="BOTTOM_RIGHT">    
-    <position height="-1" width="-1" x="535" y="139"/>    
-    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
-      sort-features="false" accessors="true" visibility="true">      
-      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
-      <operations public="true" package="true" protected="true" private="true" static="true"/>    
-    </display>  
-  </interface>  
-  <class id="2" language="java" name="com.iluwatar.NodeImpl" project="null-object" 
-    file="/null-object/src/main/java/com/iluwatar/NodeImpl.java" binary="false" corner="BOTTOM_RIGHT">    
-    <position height="-1" width="-1" x="857" y="348"/>    
-    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
-      sort-features="false" accessors="true" visibility="true">      
-      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
-      <operations public="true" package="true" protected="true" private="true" static="true"/>    
-    </display>  
-  </class>  
-  <class id="3" language="java" name="com.iluwatar.NullNode" project="null-object" 
-    file="/null-object/src/main/java/com/iluwatar/NullNode.java" binary="false" corner="BOTTOM_RIGHT">    
-    <position height="-1" width="-1" x="535" y="408"/>    
-    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
-      sort-features="false" accessors="true" visibility="true">      
-      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
-      <operations public="true" package="true" protected="true" private="true" static="true"/>    
-    </display>  
-  </class>  
-  <association id="4">    
-    <end type="SOURCE" refId="2" navigable="false">      
-      <attribute id="5" name="left"/>      
-      <multiplicity id="6" minimum="0" maximum="1"/>    
-    </end>    
-    <end type="TARGET" refId="1" navigable="true"/>    
-    <display labels="true" multiplicity="true"/>  
-  </association>  
-  <association id="7">    
-    <end type="SOURCE" refId="2" navigable="false">      
-      <attribute id="8" name="right"/>      
-      <multiplicity id="9" minimum="0" maximum="1"/>    
-    </end>    
-    <end type="TARGET" refId="1" navigable="true"/>    
-    <display labels="true" multiplicity="true"/>  
-  </association>  
-  <realization id="10">    
-    <end type="SOURCE" refId="2"/>    
-    <end type="TARGET" refId="1"/>  
-  </realization>  
-  <realization id="11">    
-    <end type="SOURCE" refId="3"/>    
-    <end type="TARGET" refId="1"/>  
-  </realization>  
-  <classifier-display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
-    sort-features="false" accessors="true" visibility="true">    
-    <attributes public="true" package="true" protected="true" private="true" static="true"/>    
-    <operations public="true" package="true" protected="true" private="true" static="true"/>  
-  </classifier-display>  
-  <association-display labels="true" multiplicity="true"/>
+<?xml version="1.0" encoding="UTF-8"?>
+<class-diagram version="1.1.8" icons="true" automaticImage="PNG" always-add-relationships="false" generalizations="true" 
+  realizations="true" associations="true" dependencies="false" nesting-relationships="true">  
+  <class id="1" language="java" name="com.iluwatar.NullNode" project="null-object" 
+    file="/null-object/src/main/java/com/iluwatar/NullNode.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="123" y="427"/>    
+    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+      sort-features="false" accessors="true" visibility="true">      
+      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
+      <operations public="true" package="true" protected="true" private="true" static="true"/>    
+    </display>  
+  </class>  
+  <interface id="2" language="java" name="com.iluwatar.Node" project="null-object" 
+    file="/null-object/src/main/java/com/iluwatar/Node.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="123" y="164"/>    
+    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+      sort-features="false" accessors="true" visibility="true">      
+      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
+      <operations public="true" package="true" protected="true" private="true" static="true"/>    
+    </display>  
+  </interface>  
+  <class id="3" language="java" name="com.iluwatar.NodeImpl" project="null-object" 
+    file="/null-object/src/main/java/com/iluwatar/NodeImpl.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="399" y="164"/>    
+    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+      sort-features="false" accessors="true" visibility="true">      
+      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
+      <operations public="true" package="true" protected="true" private="true" static="true"/>    
+    </display>  
+  </class>  
+  <association id="4">    
+    <end type="SOURCE" refId="1" navigable="false">      
+      <attribute id="5" name="instance"/>      
+      <multiplicity id="6" minimum="0" maximum="1"/>    
+    </end>    
+    <end type="TARGET" refId="1" navigable="true"/>    
+    <display labels="true" multiplicity="true"/>  
+  </association>  
+  <realization id="7">    
+    <end type="SOURCE" refId="1"/>    
+    <end type="TARGET" refId="2"/>  
+  </realization>  
+  <association id="8">    
+    <end type="SOURCE" refId="3" navigable="false">      
+      <attribute id="9" name="right"/>      
+      <multiplicity id="10" minimum="0" maximum="1"/>    
+    </end>    
+    <end type="TARGET" refId="2" navigable="true"/>    
+    <display labels="true" multiplicity="true"/>  
+  </association>  
+  <realization id="11">    
+    <end type="SOURCE" refId="3"/>    
+    <end type="TARGET" refId="2"/>  
+  </realization>  
+  <association id="12">    
+    <end type="SOURCE" refId="3" navigable="false">      
+      <attribute id="13" name="left"/>      
+      <multiplicity id="14" minimum="0" maximum="1"/>    
+    </end>    
+    <end type="TARGET" refId="2" navigable="true"/>    
+    <display labels="true" multiplicity="true"/>  
+  </association>  
+  <classifier-display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+    sort-features="false" accessors="true" visibility="true">    
+    <attributes public="true" package="true" protected="true" private="true" static="true"/>    
+    <operations public="true" package="true" protected="true" private="true" static="true"/>  
+  </classifier-display>  
+  <association-display labels="true" multiplicity="true"/>
 </class-diagram>
\ No newline at end of file
diff --git a/null-object/src/main/java/com/iluwatar/App.java b/null-object/src/main/java/com/iluwatar/App.java
index 4bba5af29..f6bef29a0 100644
--- a/null-object/src/main/java/com/iluwatar/App.java
+++ b/null-object/src/main/java/com/iluwatar/App.java
@@ -18,14 +18,14 @@ public class App
     	Node root = new NodeImpl("1",
     			new NodeImpl("11",
     					new NodeImpl("111",
-    							new NullNode(),
-    							new NullNode()),
-    					new NullNode()), 
+    							NullNode.getInstance(),
+    							NullNode.getInstance()),
+    					NullNode.getInstance()), 
     			new NodeImpl("12",
-    					new NullNode(),
+    					NullNode.getInstance(),
     					new NodeImpl("122",
-    							new NullNode(),
-    							new NullNode())));
+    							NullNode.getInstance(),
+    							NullNode.getInstance())));
 
     	root.walk();
     }
diff --git a/null-object/src/main/java/com/iluwatar/NullNode.java b/null-object/src/main/java/com/iluwatar/NullNode.java
index 5f0b440be..b63f561b4 100644
--- a/null-object/src/main/java/com/iluwatar/NullNode.java
+++ b/null-object/src/main/java/com/iluwatar/NullNode.java
@@ -1,33 +1,44 @@
-package com.iluwatar;
-
-/**
- * 
- * Null Object implementation for binary tree node.
- *
- */
-public class NullNode implements Node {
-
-	@Override
-	public int getTreeSize() {
-		return 0;
-	}
-
-	@Override
-	public Node getLeft() {
-		return null;
-	}
-
-	@Override
-	public Node getRight() {
-		return null;
-	}
-
-	@Override
-	public String getName() {
-		return null;
-	}
-
-	@Override
-	public void walk() {
-	}
-}
+package com.iluwatar;
+
+/**
+ * 
+ * Null Object implementation for binary tree node.
+ * 
+ * Implemented as Singleton, since all the NullNodes are the same.
+ *
+ */
+public class NullNode implements Node {
+
+	private static NullNode instance = new NullNode();
+	
+	private NullNode() {
+	}
+	
+	public static NullNode getInstance() {
+		return instance;
+	}
+	
+	@Override
+	public int getTreeSize() {
+		return 0;
+	}
+
+	@Override
+	public Node getLeft() {
+		return null;
+	}
+
+	@Override
+	public Node getRight() {
+		return null;
+	}
+
+	@Override
+	public String getName() {
+		return null;
+	}
+
+	@Override
+	public void walk() {
+	}
+}