add a simple example with a null logger

NullObject/Service.php

@@ -0,0 +1,30 @@
+<?php
+
+/*
+ * DesignPatternPHP
+ */
+
+namespace DesignPatterns\NullObject;
+
+/**
+ * Service is dummy service that uses a logger
+ */
+class Service
+{
+
+    protected $logger;
+
+    // we inject the logger in ctor and it is mandatory
+    public function __construct(LoggerInterface $log)
+    {
+        $this->logger = $log;
+    }
+
+    public function doSomething()
+    {
+        // no more check "if (!is_null($this->logger))..." with the NullObject pattern
+        $this->logger->log('We are in ' . __METHOD__);
+        // something to do...
+    }
+
+}