diff --git a/Behavioral/NullObject/LoggerInterface.php b/Behavioral/NullObject/LoggerInterface.php
index 99a28c7..7c1ff7d 100644
--- a/Behavioral/NullObject/LoggerInterface.php
+++ b/Behavioral/NullObject/LoggerInterface.php
@@ -3,16 +3,9 @@
 namespace DesignPatterns\Behavioral\NullObject;
 
 /**
- * LoggerInterface is a contract for logging something.
- *
- * Key feature: NullLogger MUST inherit from this interface like any other Loggers
+ * Key feature: NullLogger must inherit from this interface like any other loggers
  */
 interface LoggerInterface
 {
-    /**
-     * @param string $str
-     *
-     * @return mixed
-     */
-    public function log($str);
+    public function log(string $str);
 }
diff --git a/Behavioral/NullObject/NullLogger.php b/Behavioral/NullObject/NullLogger.php
index a4bf469..afddbd6 100644
--- a/Behavioral/NullObject/NullLogger.php
+++ b/Behavioral/NullObject/NullLogger.php
@@ -2,19 +2,9 @@
 
 namespace DesignPatterns\Behavioral\NullObject;
 
-/**
- * Performance concerns : ok there is a call for nothing but we spare an "if is_null"
- * I didn't run a benchmark but I think it's equivalent.
- *
- * Key feature : of course this logger MUST implement the same interface (or abstract)
- * like the other loggers.
- */
 class NullLogger implements LoggerInterface
 {
-    /**
-     * {@inheritdoc}
-     */
-    public function log($str)
+    public function log(string $str)
     {
         // do nothing
     }
diff --git a/Behavioral/NullObject/PrintLogger.php b/Behavioral/NullObject/PrintLogger.php
index 371c1ab..6c1d4ba 100644
--- a/Behavioral/NullObject/PrintLogger.php
+++ b/Behavioral/NullObject/PrintLogger.php
@@ -2,15 +2,9 @@
 
 namespace DesignPatterns\Behavioral\NullObject;
 
-/**
- * PrintLogger is a logger that prints the log entry to standard output.
- */
 class PrintLogger implements LoggerInterface
 {
-    /**
-     * @param string $str
-     */
-    public function log($str)
+    public function log(string $str)
     {
         echo $str;
     }
diff --git a/Behavioral/NullObject/Service.php b/Behavioral/NullObject/Service.php
index 56a3847..81baf8f 100644
--- a/Behavioral/NullObject/Service.php
+++ b/Behavioral/NullObject/Service.php
@@ -2,24 +2,19 @@
 
 namespace DesignPatterns\Behavioral\NullObject;
 
-/**
- * Service is dummy service that uses a logger.
- */
 class Service
 {
     /**
      * @var LoggerInterface
      */
-    protected $logger;
+    private $logger;
 
     /**
-     * we inject the logger in ctor and it is mandatory.
-     *
-     * @param LoggerInterface $log
+     * @param LoggerInterface $logger
      */
-    public function __construct(LoggerInterface $log)
+    public function __construct(LoggerInterface $logger)
     {
-        $this->logger = $log;
+        $this->logger = $logger;
     }
 
     /**
@@ -27,8 +22,7 @@ class Service
      */
     public function doSomething()
     {
-        // no more check "if (!is_null($this->logger))..." with the NullObject pattern
+        // notice here that you don't have to check if the logger is set with eg. is_null(), instead just use it
         $this->logger->log('We are in '.__METHOD__);
-        // something to do...
     }
 }
diff --git a/Behavioral/NullObject/Tests/LoggerTest.php b/Behavioral/NullObject/Tests/LoggerTest.php
index 034b577..0e35aa5 100644
--- a/Behavioral/NullObject/Tests/LoggerTest.php
+++ b/Behavioral/NullObject/Tests/LoggerTest.php
@@ -6,17 +6,12 @@ use DesignPatterns\Behavioral\NullObject\NullLogger;
 use DesignPatterns\Behavioral\NullObject\PrintLogger;
 use DesignPatterns\Behavioral\NullObject\Service;
 
-/**
- * LoggerTest tests for different loggers.
- */
 class LoggerTest extends \PHPUnit_Framework_TestCase
 {
     public function testNullObject()
     {
-        // one can use a singleton for NullObjet : I don't think it's a good idea
-        // because the purpose behind null object is to "avoid special case".
         $service = new Service(new NullLogger());
-        $this->expectOutputString(null);  // no output
+        $this->expectOutputString(null);
         $service->doSomething();
     }