diff --git a/composer.json b/composer.json
index aa0a00f..c0eb884 100644
--- a/composer.json
+++ b/composer.json
@@ -17,7 +17,7 @@
     "psr/link": "~1.0"
   },
   "require-dev": {
-    "phpunit/phpunit": "^7.0 || ^6.4 || ^5.7 || ^4.8.35"
+    "phpunit/phpunit": "^9.0 || ^7.0 || ^6.4 || ^5.7 || ^4.8.35"
   },
   "minimum-stability": "dev",
   "autoload": {
diff --git a/src/Hal.php b/src/Hal.php
index 5b42976..2c93be4 100644
--- a/src/Hal.php
+++ b/src/Hal.php
@@ -179,11 +179,11 @@ public function addHalLink($rel, HalLink $link, $forceArray = false)
      * Add an embedded resource, identified by $rel and represented by $resource.
      *
      * @param string $rel
-     * @param \Nocarrier\Hal $resource
+     * @param \Nocarrier\Hal|null $resource
      *
      * @return \Nocarrier\Hal
      */
-    public function addResource($rel, \Nocarrier\Hal $resource = null, $forceArray = true)
+    public function addResource($rel, $resource = null, $forceArray = true)
     {
         if (!is_string($rel)) {
             throw new \InvalidArgumentException(
@@ -231,7 +231,7 @@ public function setResource($rel, $resource)
     /**
      * Set resource's data
      */
-    public function setData(Array $data = null)
+    public function setData($data = null)
     {
         $this->data = $data;
         return $this;
diff --git a/src/HalJsonRenderer.php b/src/HalJsonRenderer.php
index 0398721..1bb7dbe 100644
--- a/src/HalJsonRenderer.php
+++ b/src/HalJsonRenderer.php
@@ -135,15 +135,17 @@ protected function stripAttributeMarker(array $data)
      * Return an array (compatible with the hal+json format) representing the
      * complete response.
      *
-     * @param \Nocarrier\Hal $resource
+     * @param \Nocarrier\Hal|null $resource
      * @return array
      */
-    protected function arrayForJson(Hal $resource = null)
+    protected function arrayForJson($resource = null)
     {
         if ($resource == null) {
             return array();
         }
 
+        assert($resource instanceof Hal);
+
         $data = $resource->getData();
         if ($resource->getShouldStripAttributes()) {
             $data = $this->stripAttributeMarker($data);
diff --git a/tests/Hal/HalTest.php b/tests/Hal/HalTest.php
index 241c297..d9e739b 100644
--- a/tests/Hal/HalTest.php
+++ b/tests/Hal/HalTest.php
@@ -102,7 +102,7 @@ public function testResourceJsonResponse()
 
         $resource = json_decode($hal->asJson());
         $this->assertInstanceOf('StdClass', $resource->_embedded);
-        $this->assertInternalType('array', $resource->_embedded->resource);
+        $this->assertIsArray( $resource->_embedded->resource);
         $this->assertEquals($resource->_embedded->resource[0]->_links->self->href, '/resource/1');
         $this->assertEquals($resource->_embedded->resource[0]->field1, 'value1');
         $this->assertEquals($resource->_embedded->resource[0]->field2, 'value2');
@@ -150,7 +150,7 @@ public function testEmbeddedResourceInResourceJsonResponse()
 
         $hal->addResource('resource', $res);
         $result = json_decode($hal->asJson());
-        $this->assertInternalType('array', $result->_embedded->resource[0]->_embedded->item);
+        $this->assertIsArray( $result->_embedded->resource[0]->_embedded->item);
         $this->assertEquals('/resource/1/item/1', $result->_embedded->resource[0]->_embedded->item[0]->_links->self->href);
         $this->assertEquals('itemValue1', $result->_embedded->resource[0]->_embedded->item[0]->itemField1);
     }
@@ -513,7 +513,7 @@ public function testAddCurieConformsToSpecification()
         $x = new Hal('/orders');
         $x->addCurie('acme', 'http://docs.acme.com/relations/{rel}');
         $obj = json_decode($x->asJson());
-        $this->assertInternalType('array', $obj->_links->curies);
+        $this->assertIsArray( $obj->_links->curies);
         $this->assertTrue($obj->_links->curies[0]->templated);
         $this->assertEquals('acme', $obj->_links->curies[0]->name);
         $this->assertEquals('http://docs.acme.com/relations/{rel}', $obj->_links->curies[0]->href);
@@ -624,7 +624,7 @@ public function testSetResourceWithArrayOfResources()
 
         $resource = json_decode($hal->asJson());
         $this->assertInstanceOf('StdClass', $resource->_embedded);
-        $this->assertInternalType('array', $resource->_embedded->resource);
+        $this->assertIsArray( $resource->_embedded->resource);
         $this->assertEquals($resource->_embedded->resource[0]->field1, '1');
         $this->assertEquals($resource->_embedded->resource[1]->field1, '2');
     }
@@ -735,11 +735,9 @@ public function testGetFirstResourceReturnsFirstOfMultipleItems()
         $this->assertEquals($res1, $hal->getFirstResource("resource"));
     }
 
-    /**
-     * @expectedException RuntimeException
-     */
     public function testHalFromJsonThrowsExceptionOnInvalidJSON()
     {
+        $this->expectException('RuntimeException');
         $invalidJson = 'foo';
         Hal::fromJson($invalidJson);
     }
@@ -786,7 +784,7 @@ public function testEmbeddingResourceWithSingleElement()
         );
 
         $json = json_decode($hal->asJson());
-        $this->assertInternalType('array', $json->_embedded->foo->_embedded->bar);
+        $this->assertIsArray( $json->_embedded->foo->_embedded->bar);
     }
 
     public function testErrorAddResource()