diff --git a/phpunit.xml b/phpunit.xml
index 3ac414c..14b4e57 100644
--- a/phpunit.xml
+++ b/phpunit.xml
@@ -4,7 +4,7 @@
     </php>
     <filter>
         <whitelist addUncoveredFilesFromWhitelist="true">
-            <directory>./webfiori</directory>
+            <directory>./webfiori/json</directory>
         </whitelist>
     </filter>
     <logging>
@@ -12,7 +12,7 @@
     </logging>
     <testsuites>
         <testsuite name="Json Tests">
-            <directory>./tests</directory>
+            <directory>./tests/webfiori/tests/json</directory>
         </testsuite>
     </testsuites>
 </phpunit>
\ No newline at end of file
diff --git a/tests/JsonConverterTest.php b/tests/webfiori/tests/json/JsonConverterTest.php
similarity index 99%
rename from tests/JsonConverterTest.php
rename to tests/webfiori/tests/json/JsonConverterTest.php
index 1c3d536..3713cc1 100644
--- a/tests/JsonConverterTest.php
+++ b/tests/webfiori/tests/json/JsonConverterTest.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace jsonx\tests;
+namespace webfiori\tests\json;
 
 use webfiori\json\Json;
 use jsonx\tests\Obj0;
diff --git a/tests/JsonTest.php b/tests/webfiori/tests/json/JsonTest.php
similarity index 96%
rename from tests/JsonTest.php
rename to tests/webfiori/tests/json/JsonTest.php
index 0bfa61e..6b2e4c1 100644
--- a/tests/JsonTest.php
+++ b/tests/webfiori/tests/json/JsonTest.php
@@ -1,4 +1,5 @@
 <?php
+namespace webfiori\tests\json;
 
 use webfiori\json\Json;
 use jsonx\tests\Obj0;
@@ -735,9 +736,11 @@ public function testAdd04() {
      */
     public function testAdd05() {
         $j = new Json();
-        $this->assertFalse($j->add('  ',null));
         $this->assertTrue($j->add('null-value',null));
         $this->assertEquals('{"null-value":null}',$j->toJSONString());
+        $this->expectException(\InvalidArgumentException::class);
+        $this->assertFalse($j->add('  ',null));
+        
     }
     /**
      * @test
@@ -814,6 +817,43 @@ public function testAdd09() {
         $j->addNumber('one', 1);
         $this->assertEquals(1, $j->get('one'));
     }
+    /**
+     * @test
+     */
+    public function testAdd10() {
+        $j = new Json();
+        $j->add('one', 'one');
+        $this->assertEquals(1, count($j->getPropsNames()));
+        $j->add('one', null);
+        $this->assertEquals(1, count($j->getPropsNames()));
+        $this->assertNull($j->get('one'));
+    }
+    /**
+     * @test
+     */
+    public function testAddNull00() {
+        $j = new Json();
+        $this->assertTrue($j->addNull('null'));
+        $this->assertNull($j->get('null'));
+    }
+    /**
+     * @test
+     */
+    public function testAddNull01() {
+        $j = new Json();
+        $this->expectException(\InvalidArgumentException::class);
+        $this->assertTrue($j->addNull(' '));
+    }
+    /**
+     * @test
+     */
+    public function testAddNull02() {
+        $j = new Json();
+        $j->addString('not-null', 'Hello');
+        $this->assertEquals('Hello', $j->get('not-null'));
+        $this->assertTrue($j->addNull('not-null'));
+        $this->assertNull($j->get('not-null'));
+    }
     /**
      * @test
      */
@@ -976,7 +1016,19 @@ public function testAddObj02() {
     /**
      * @test
      */
-    public function testAddStringTest00() {
+    public function testAddObj03() {
+        $j = new Json();
+        $obj = new Obj1('Hello',0,true,null,'he');
+        $j->addString('object','An Obj');
+        $this->assertEquals('An Obj', $j->get('object'));
+        $j->addObject('object', $obj);
+        $this->assertEquals('{"object":{"property-00":"Hello","property-01":0,"property-02":true}}',$j.'');
+    }
+    /**
+     * @test
+     */
+    public function testAddString00() {
+        $this->expectException(\InvalidArgumentException::class);
         $j = new Json();
         $this->assertFalse($j->addString('','Hello World!'));
         $this->assertFalse($j->addString('  ','Hello World!'));
@@ -986,18 +1038,30 @@ public function testAddStringTest00() {
     /**
      * @test
      */
-    public function testAddStringTest01() {
+    public function testAddString01() {
         $j = new Json();
         $this->assertTrue($j->addString('hello','Hello World!'));
         $this->assertEquals('{"hello":"Hello World!"}',$j.'');
+        $this->assertFalse($j->addString('a-number', 33));
     }
     /**
      * @test
      */
-    public function testAddStringTest02() {
+    public function testAddString02() {
         $j = new Json();
         $this->assertFalse($j->addBoolean('invalid-boolean','falseX'));
     }
+    /**
+     * @test
+     */
+    public function testAddString03() {
+        $j = new Json();
+        $j->addNumber('a-number', 33);
+        $this->assertSame(33, $j->get('a-number'));
+        $j->addString('a-number', '33');
+        $this->assertNotSame(33, $j->get('a-number'));
+        $this->assertEquals('33', $j->get('a-number'));
+    }
     /**
      * @test
      */
diff --git a/tests/PropertyTest.php b/tests/webfiori/tests/json/PropertyTest.php
similarity index 99%
rename from tests/PropertyTest.php
rename to tests/webfiori/tests/json/PropertyTest.php
index 5f658d1..d2c4120 100644
--- a/tests/PropertyTest.php
+++ b/tests/webfiori/tests/json/PropertyTest.php
@@ -1,5 +1,5 @@
 <?php
-namespace jsonx\tests;
+namespace webfiori\tests\json;
 
 use webfiori\json\Json;
 use jsonx\tests\Obj0;
diff --git a/webfiori/json/Json.php b/webfiori/json/Json.php
index 16273ae..ed17eb0 100644
--- a/webfiori/json/Json.php
+++ b/webfiori/json/Json.php
@@ -172,12 +172,13 @@ public function __toString() {
         return $this->toJSONString();
     }
     /**
-     * Adds a new value to the JSON string.
+     * Adds a new value to JSON.
      * 
      * This method can be used to add an integer, a double, 
      * a string, an array or an object. If null is given, the method will 
      * set the value at the given key to null. If the given value or key is 
      * invalid, the method will not add the value and will return false.
+     * This method also can be used to update the value of an existing property.
      * 
      * @param string $key The value of the key.
      * 
@@ -193,31 +194,21 @@ public function __toString() {
      * @since 1.1
      */
     public function add(string $key, $value, $arrayAsObj = false) {
-        if ($value !== null) {
-            if (!$this->updateExisting($key, $value)) {
-                return $this->addString($key, $value) ||
-                $this->addArray($key, $value, $arrayAsObj) ||
-                $this->addBoolean($key, $value) ||
-                $this->addNumber($key, $value) || 
-                $this->addObject($key, $value);
-            }
-            $this->getProperty($key)->setAsObject($arrayAsObj);
-            return true;
-        } else {
-            $prop = $this->createProb($key, $value);
-
-            if ($prop !== null) {
-                $this->propsArr[] = $prop;
-
-                return true;
-            }
+        if (!$this->updateExisting($key, $value)) {
+            return $this->addString($key, $value) ||
+            $this->addArray($key, $value, $arrayAsObj) ||
+            $this->addBoolean($key, $value) ||
+            $this->addNumber($key, $value) || 
+            $this->addObject($key, $value) ||
+            $this->addNull($key);
         }
-
-        return false;
+        return true;
     }
     /**
      * Adds an array to the JSON.
      * 
+     * This method also can be used to update the value of an existing property.
+     * 
      * @param string $key The name of the key.
      * 
      * @param array $value The array that will be added.
@@ -234,7 +225,7 @@ public function addArray(string $key, $value, $asObject = false) {
             $prop = $this->createProb($key, $value);
             $propType = $prop->getType();
 
-            if ($prop !== null && $propType == JsonTypes::ARR) {
+            if ($propType == JsonTypes::ARR) {
                 $prop->setAsObject($asObject);
                 $this->propsArr[] = $prop;
 
@@ -244,12 +235,15 @@ public function addArray(string $key, $value, $asObject = false) {
             return false;
         } else {
             $this->getProperty($key)->setAsObject($asObject);
+
             return true;
         }
     }
     /**
      * Adds a boolean value (true or false) to the JSON data.
      * 
+     * This method also can be used to update the value of an existing property.
+     * 
      * @param string $key The name of the key.
      * 
      * @param boolean $val true or false. If not specified, 
@@ -265,7 +259,7 @@ public function addBoolean($key, $val = true) {
         if (!$this->updateExisting($key, $val)) {
             $prop = $this->createProb($key, $val);
 
-            if ($prop !== null && $prop->getType() == 'boolean') {
+            if ($prop->getType() == 'boolean') {
                 $this->propsArr[] = $prop;
 
                 return true;
@@ -273,6 +267,7 @@ public function addBoolean($key, $val = true) {
 
             return false;
         }
+
         return true;
     }
     /**
@@ -290,12 +285,41 @@ public function addMultiple(array $arr) {
             $this->add($key, $value);
         }
     }
+    /**
+     * Adds a 'null' value to JSON.
+     * 
+     * This method also can be used to update the value of an existing property.
+     * 
+     * @param string $key The name of value key.
+     * 
+     * @return boolean The method will return true if the value is set. 
+     * If the given value or key is invalid, the method will return false.
+     */
+    public function addNull(string $key) {
+        $nul = null;
+
+        if (!$this->updateExisting($key, $nul)) {
+            $prop = $this->createProb($key, $nul);
+            $propType = $prop->getType();
+
+            if ($propType == JsonTypes::NUL) {
+                $this->propsArr[] = $prop;
+
+                return true;
+            }
+
+            return false;
+        }
+
+        return true;
+    }
     /**
      * Adds a number to the JSON data.
      * 
      * Note that if the given number is the constant <b>INF</b> or the constant 
      * <b>NAN</b>, The method will add them as a string. The 'INF' will be added
      * as the string "Infinity" and the 'NAN' will be added as the string "Nan".
+     * This method also can be used to update the value of an existing property.
      * 
      * @param string $key The name of the key.
      * 
@@ -313,7 +337,7 @@ public function addNumber(string $key, $value) {
             $prop = $this->createProb($key, $value);
             $propType = $prop->getType();
 
-            if ($prop !== null && $propType == JsonTypes::INT || $propType == JsonTypes::DOUBLE) {
+            if ($propType == JsonTypes::INT || $propType == JsonTypes::DOUBLE) {
                 $this->propsArr[] = $prop;
 
                 return true;
@@ -321,6 +345,7 @@ public function addNumber(string $key, $value) {
 
             return false;
         }
+
         return true;
     }
     /**
@@ -335,6 +360,7 @@ public function addNumber(string $key, $value) {
      * <code>getFirstProp()</code> and <code>getSecondProp()</code>. 
      * In that case, the generated JSON will be on the formate 
      * <b>{"FirstProp":"prop-1","SecondProp":""}</b>.
+     * This method also can be used to update the value of an existing property.
      * 
      * @param string $key The key value.
      * 
@@ -345,12 +371,12 @@ public function addNumber(string $key, $value) {
      * 
      * @since 1.0
      */
-    public function addObject(string $key, $val) {
+    public function addObject(string $key, &$val) {
         if (!$this->updateExisting($key, $val)) {
             $prop = $this->createProb($key, $val);
             $propType = $prop->getType();
 
-            if ($prop !== null && $propType == JsonTypes::OBJ) {
+            if ($propType == JsonTypes::OBJ) {
                 $this->propsArr[] = $prop;
 
                 return true;
@@ -358,11 +384,14 @@ public function addObject(string $key, $val) {
 
             return false;
         }
+
         return true;
     }
     /**
      * Adds a new key to the JSON data with its value as string.
      * 
+     * This method also can be used to update the value of an existing property.
+     * 
      * @param string $key The name of the key. Must be non empty string.
      * 
      * @param string $val The value of the string.
@@ -377,7 +406,7 @@ public function addString(string $key, $val) {
         if (!$this->updateExisting($key, $val)) {
             $prop = $this->createProb($key, $val);
 
-            if ($prop !== null && $prop->getType() == JsonTypes::STRING) {
+            if ($prop->getType() == JsonTypes::STRING) {
                 $this->propsArr[] = $prop;
 
                 return true;
@@ -385,19 +414,9 @@ public function addString(string $key, $val) {
 
             return false;
         }
+
         return true;
     }
-    private function updateExisting($key, $val) {
-        $tempProp = $this->getProperty($key);
-        
-        if ($tempProp !== null) {
-            $tempProp->setValue($val);
-            
-            return true;
-        }
-        
-        return false;
-    }
 
     /**
      * Converts a JSON-like string to JSON object.
@@ -764,8 +783,19 @@ private function _setIsFormattedArray(&$arr) {
     private function createProb($name, $value) {
         try {
             return new Property($name, $value, $this->getPropStyle());
-        } catch (\Exception $ex) {
-            return null;
+        } catch (InvalidArgumentException $ex) {
+            throw new InvalidArgumentException($ex->getMessage(), $ex->getCode(), $ex);
+        }
+    }
+    private function updateExisting($key, &$val) {
+        $tempProp = $this->getProperty($key);
+
+        if ($tempProp !== null) {
+            $tempProp->setValue($val);
+
+            return true;
         }
+
+        return false;
     }
 }
diff --git a/webfiori/json/Property.php b/webfiori/json/Property.php
index 5dc3798..6250512 100644
--- a/webfiori/json/Property.php
+++ b/webfiori/json/Property.php
@@ -86,17 +86,18 @@ class Property {
     public function __construct(string $name, $value, $style = null) {
         $this->name = '';
         $this->setStyle('none');
+
         if (!$this->setName($name)) {
             throw new InvalidArgumentException('Invalid property name: "'.$name.'"');
         }
-        
+
         $this->setAsObject(false);
 
         if ($style !== null) {
             $this->setStyle($style);
         }
 
-        
+
         $this->setValue($value);
     }
     /**
@@ -121,7 +122,7 @@ public function &getValue() {
     public function getJsonXTagName() : string {
         $type = $this->getType();
         $retVal = '';
-        
+
         if ($type == JsonTypes::ARR) {
             if ($this->isAsObject()) {
                 $retVal = 'json:object';
@@ -143,7 +144,7 @@ public function getJsonXTagName() : string {
         } else {
             $retVal = 'json:null';
         } 
-        
+
         return $retVal;
     }
     /**