diff --git a/composer.json b/composer.json
index 63ae8cb..59ebc4c 100644
--- a/composer.json
+++ b/composer.json
@@ -11,7 +11,8 @@
     ],
     "require": {
         "php": ">=7.0",
-        "nesbot/carbon": "~1.20"
+        "nesbot/carbon": "~1.20",
+        "symfony/var-dumper": "~3.3"
     },
     "require-dev": {
         "mockery/mockery": "~1.0",
@@ -27,9 +28,6 @@
             "Tightenco\\": "src/Tightenco"
         }
     },
-    "suggest": {
-        "symfony/var-dumper": "Required to prettify dd() and dump() (~3.3)."
-    },
     "scripts": {
         "test": [
             "@composer install",
diff --git a/composer.lock b/composer.lock
index bfd25ac..023cee4 100644
--- a/composer.lock
+++ b/composer.lock
@@ -4,7 +4,7 @@
         "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#composer-lock-the-lock-file",
         "This file is @generated automatically"
     ],
-    "content-hash": "679e3042bfdf42a1f874e734d08033b1",
+    "content-hash": "3b0035f594bd16fe9ad9d04825982dce",
     "packages": [
         {
             "name": "nesbot/carbon",
@@ -61,16 +61,16 @@
         },
         {
             "name": "symfony/polyfill-mbstring",
-            "version": "v1.6.0",
+            "version": "v1.7.0",
             "source": {
                 "type": "git",
                 "url": "https://github.com/symfony/polyfill-mbstring.git",
-                "reference": "2ec8b39c38cb16674bbf3fea2b6ce5bf117e1296"
+                "reference": "78be803ce01e55d3491c1397cf1c64beb9c1b63b"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/symfony/polyfill-mbstring/zipball/2ec8b39c38cb16674bbf3fea2b6ce5bf117e1296",
-                "reference": "2ec8b39c38cb16674bbf3fea2b6ce5bf117e1296",
+                "url": "https://api.github.com/repos/symfony/polyfill-mbstring/zipball/78be803ce01e55d3491c1397cf1c64beb9c1b63b",
+                "reference": "78be803ce01e55d3491c1397cf1c64beb9c1b63b",
                 "shasum": ""
             },
             "require": {
@@ -82,7 +82,7 @@
             "type": "library",
             "extra": {
                 "branch-alias": {
-                    "dev-master": "1.6-dev"
+                    "dev-master": "1.7-dev"
                 }
             },
             "autoload": {
@@ -116,20 +116,20 @@
                 "portable",
                 "shim"
             ],
-            "time": "2017-10-11T12:05:26+00:00"
+            "time": "2018-01-30T19:27:44+00:00"
         },
         {
             "name": "symfony/translation",
-            "version": "v3.4.2",
+            "version": "v3.4.4",
             "source": {
                 "type": "git",
                 "url": "https://github.com/symfony/translation.git",
-                "reference": "4c5d5582baf2829751a5207659329c1f52eedeb6"
+                "reference": "10b32cf0eae28b9b39fe26c456c42b19854c4b84"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/symfony/translation/zipball/4c5d5582baf2829751a5207659329c1f52eedeb6",
-                "reference": "4c5d5582baf2829751a5207659329c1f52eedeb6",
+                "url": "https://api.github.com/repos/symfony/translation/zipball/10b32cf0eae28b9b39fe26c456c42b19854c4b84",
+                "reference": "10b32cf0eae28b9b39fe26c456c42b19854c4b84",
                 "shasum": ""
             },
             "require": {
@@ -184,7 +184,76 @@
             ],
             "description": "Symfony Translation Component",
             "homepage": "https://symfony.com",
-            "time": "2017-12-12T08:27:14+00:00"
+            "time": "2018-01-18T22:16:57+00:00"
+        },
+        {
+            "name": "symfony/var-dumper",
+            "version": "v3.4.4",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/symfony/var-dumper.git",
+                "reference": "472a9849930cf21f73abdb02240f17cf5b5bd1a7"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/symfony/var-dumper/zipball/472a9849930cf21f73abdb02240f17cf5b5bd1a7",
+                "reference": "472a9849930cf21f73abdb02240f17cf5b5bd1a7",
+                "shasum": ""
+            },
+            "require": {
+                "php": "^5.5.9|>=7.0.8",
+                "symfony/polyfill-mbstring": "~1.0"
+            },
+            "conflict": {
+                "phpunit/phpunit": "<4.8.35|<5.4.3,>=5.0"
+            },
+            "require-dev": {
+                "ext-iconv": "*",
+                "twig/twig": "~1.34|~2.4"
+            },
+            "suggest": {
+                "ext-iconv": "To convert non-UTF-8 strings to UTF-8 (or symfony/polyfill-iconv in case ext-iconv cannot be used).",
+                "ext-intl": "To show region name in time zone dump",
+                "ext-symfony_debug": ""
+            },
+            "type": "library",
+            "extra": {
+                "branch-alias": {
+                    "dev-master": "3.4-dev"
+                }
+            },
+            "autoload": {
+                "files": [
+                    "Resources/functions/dump.php"
+                ],
+                "psr-4": {
+                    "Symfony\\Component\\VarDumper\\": ""
+                },
+                "exclude-from-classmap": [
+                    "/Tests/"
+                ]
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "authors": [
+                {
+                    "name": "Nicolas Grekas",
+                    "email": "p@tchwork.com"
+                },
+                {
+                    "name": "Symfony Community",
+                    "homepage": "https://symfony.com/contributors"
+                }
+            ],
+            "description": "Symfony mechanism for exploring and dumping PHP variables",
+            "homepage": "https://symfony.com",
+            "keywords": [
+                "debug",
+                "dump"
+            ],
+            "time": "2018-01-29T09:03:43+00:00"
         }
     ],
     "packages-dev": [
@@ -558,16 +627,16 @@
         },
         {
             "name": "phpdocumentor/reflection-docblock",
-            "version": "4.2.0",
+            "version": "4.3.0",
             "source": {
                 "type": "git",
                 "url": "https://github.com/phpDocumentor/ReflectionDocBlock.git",
-                "reference": "66465776cfc249844bde6d117abff1d22e06c2da"
+                "reference": "94fd0001232e47129dd3504189fa1c7225010d08"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/phpDocumentor/ReflectionDocBlock/zipball/66465776cfc249844bde6d117abff1d22e06c2da",
-                "reference": "66465776cfc249844bde6d117abff1d22e06c2da",
+                "url": "https://api.github.com/repos/phpDocumentor/ReflectionDocBlock/zipball/94fd0001232e47129dd3504189fa1c7225010d08",
+                "reference": "94fd0001232e47129dd3504189fa1c7225010d08",
                 "shasum": ""
             },
             "require": {
@@ -605,7 +674,7 @@
                 }
             ],
             "description": "With this component, a library can provide support for annotations via DocBlocks or otherwise retrieve information that is embedded in a DocBlock.",
-            "time": "2017-11-27T17:38:31+00:00"
+            "time": "2017-11-30T07:14:17+00:00"
         },
         {
             "name": "phpdocumentor/type-resolver",
@@ -1052,16 +1121,16 @@
         },
         {
             "name": "phpunit/phpunit-mock-objects",
-            "version": "5.0.5",
+            "version": "5.0.6",
             "source": {
                 "type": "git",
                 "url": "https://github.com/sebastianbergmann/phpunit-mock-objects.git",
-                "reference": "283b9f4f670e3a6fd6c4ff95c51a952eb5c75933"
+                "reference": "33fd41a76e746b8fa96d00b49a23dadfa8334cdf"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/sebastianbergmann/phpunit-mock-objects/zipball/283b9f4f670e3a6fd6c4ff95c51a952eb5c75933",
-                "reference": "283b9f4f670e3a6fd6c4ff95c51a952eb5c75933",
+                "url": "https://api.github.com/repos/sebastianbergmann/phpunit-mock-objects/zipball/33fd41a76e746b8fa96d00b49a23dadfa8334cdf",
+                "reference": "33fd41a76e746b8fa96d00b49a23dadfa8334cdf",
                 "shasum": ""
             },
             "require": {
@@ -1107,7 +1176,7 @@
                 "mock",
                 "xunit"
             ],
-            "time": "2017-12-10T08:01:53+00:00"
+            "time": "2018-01-06T05:45:45+00:00"
         },
         {
             "name": "sebastian/code-unit-reverse-lookup",
@@ -1156,16 +1225,16 @@
         },
         {
             "name": "sebastian/comparator",
-            "version": "2.1.0",
+            "version": "2.1.2",
             "source": {
                 "type": "git",
                 "url": "https://github.com/sebastianbergmann/comparator.git",
-                "reference": "1174d9018191e93cb9d719edec01257fc05f8158"
+                "reference": "11c07feade1d65453e06df3b3b90171d6d982087"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/sebastianbergmann/comparator/zipball/1174d9018191e93cb9d719edec01257fc05f8158",
-                "reference": "1174d9018191e93cb9d719edec01257fc05f8158",
+                "url": "https://api.github.com/repos/sebastianbergmann/comparator/zipball/11c07feade1d65453e06df3b3b90171d6d982087",
+                "reference": "11c07feade1d65453e06df3b3b90171d6d982087",
                 "shasum": ""
             },
             "require": {
@@ -1216,7 +1285,7 @@
                 "compare",
                 "equality"
             ],
-            "time": "2017-11-03T07:16:52+00:00"
+            "time": "2018-01-12T06:34:42+00:00"
         },
         {
             "name": "sebastian/diff",
@@ -1668,75 +1737,6 @@
             "homepage": "https://github.com/sebastianbergmann/version",
             "time": "2016-10-03T07:35:21+00:00"
         },
-        {
-            "name": "symfony/var-dumper",
-            "version": "v3.4.2",
-            "source": {
-                "type": "git",
-                "url": "https://github.com/symfony/var-dumper.git",
-                "reference": "757074cf71b952ce9e75b557538948811c2bf006"
-            },
-            "dist": {
-                "type": "zip",
-                "url": "https://api.github.com/repos/symfony/var-dumper/zipball/757074cf71b952ce9e75b557538948811c2bf006",
-                "reference": "757074cf71b952ce9e75b557538948811c2bf006",
-                "shasum": ""
-            },
-            "require": {
-                "php": "^5.5.9|>=7.0.8",
-                "symfony/polyfill-mbstring": "~1.0"
-            },
-            "conflict": {
-                "phpunit/phpunit": "<4.8.35|<5.4.3,>=5.0"
-            },
-            "require-dev": {
-                "ext-iconv": "*",
-                "twig/twig": "~1.34|~2.4"
-            },
-            "suggest": {
-                "ext-iconv": "To convert non-UTF-8 strings to UTF-8 (or symfony/polyfill-iconv in case ext-iconv cannot be used).",
-                "ext-intl": "To show region name in time zone dump",
-                "ext-symfony_debug": ""
-            },
-            "type": "library",
-            "extra": {
-                "branch-alias": {
-                    "dev-master": "3.4-dev"
-                }
-            },
-            "autoload": {
-                "files": [
-                    "Resources/functions/dump.php"
-                ],
-                "psr-4": {
-                    "Symfony\\Component\\VarDumper\\": ""
-                },
-                "exclude-from-classmap": [
-                    "/Tests/"
-                ]
-            },
-            "notification-url": "https://packagist.org/downloads/",
-            "license": [
-                "MIT"
-            ],
-            "authors": [
-                {
-                    "name": "Nicolas Grekas",
-                    "email": "p@tchwork.com"
-                },
-                {
-                    "name": "Symfony Community",
-                    "homepage": "https://symfony.com/contributors"
-                }
-            ],
-            "description": "Symfony mechanism for exploring and dumping PHP variables",
-            "homepage": "https://symfony.com",
-            "keywords": [
-                "debug",
-                "dump"
-            ],
-            "time": "2017-12-11T22:06:16+00:00"
-        },
         {
             "name": "theseer/tokenizer",
             "version": "1.1.0",
@@ -1779,16 +1779,16 @@
         },
         {
             "name": "webmozart/assert",
-            "version": "1.2.0",
+            "version": "1.3.0",
             "source": {
                 "type": "git",
                 "url": "https://github.com/webmozart/assert.git",
-                "reference": "2db61e59ff05fe5126d152bd0655c9ea113e550f"
+                "reference": "0df1908962e7a3071564e857d86874dad1ef204a"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/webmozart/assert/zipball/2db61e59ff05fe5126d152bd0655c9ea113e550f",
-                "reference": "2db61e59ff05fe5126d152bd0655c9ea113e550f",
+                "url": "https://api.github.com/repos/webmozart/assert/zipball/0df1908962e7a3071564e857d86874dad1ef204a",
+                "reference": "0df1908962e7a3071564e857d86874dad1ef204a",
                 "shasum": ""
             },
             "require": {
@@ -1825,7 +1825,7 @@
                 "check",
                 "validate"
             ],
-            "time": "2016-11-23T20:04:58+00:00"
+            "time": "2018-01-29T19:49:41+00:00"
         }
     ],
     "aliases": [],
diff --git a/src/Tightenco/Support/Collection.php b/src/Tightenco/Support/Collection.php
index 6625875..22fd5f7 100644
--- a/src/Tightenco/Support/Collection.php
+++ b/src/Tightenco/Support/Collection.php
@@ -271,6 +271,8 @@ public function crossJoin(...$lists)
      */
     public function dd(...$args)
     {
+        http_response_code(500);
+
         call_user_func_array([$this, 'dump'], $args);
 
         die(1);
@@ -391,7 +393,7 @@ public function every($key, $operator = null, $value = null)
     public function except($keys)
     {
         if ($keys instanceof self) {
-            $keys = $keys->keys()->all();
+            $keys = $keys->all();
         } elseif (! is_array($keys)) {
             $keys = func_get_args();
         }
@@ -658,6 +660,12 @@ public function get($key, $default = null)
      */
     public function groupBy($groupBy, $preserveKeys = false)
     {
+        if (is_array($groupBy)) {
+            $nextGroups = $groupBy;
+
+            $groupBy = array_shift($nextGroups);
+        }
+
         $groupBy = $this->valueRetriever($groupBy);
 
         $results = [];
@@ -680,7 +688,13 @@ public function groupBy($groupBy, $preserveKeys = false)
             }
         }
 
-        return new static($results);
+        $result = new static($results);
+
+        if (! empty($nextGroups)) {
+            return $result->map->groupBy($nextGroups, $preserveKeys);
+        }
+
+        return $result;
     }
 
     /**
@@ -1052,6 +1066,10 @@ public function only($keys)
             return new static($this->items);
         }
 
+        if ($keys instanceof self) {
+            $keys = $keys->all();
+        }
+
         $keys = is_array($keys) ? $keys : func_get_args();
 
         return new static(Arr::only($this->items, $keys));
diff --git a/src/Tightenco/Support/alias.php b/src/Tightenco/Support/alias.php
index 696c9f5..7bdb211 100644
--- a/src/Tightenco/Support/alias.php
+++ b/src/Tightenco/Support/alias.php
@@ -1,20 +1,35 @@
 <?php
 
 $aliases = [
-    Illuminate\Support\Collection::class => Tightenco\Support\Collection::class,
-    Illuminate\Support\Arr::class => Tightenco\Support\Arr::class,
-    Illuminate\Support\Carbon::class => Tightenco\Support\Carbon::class,
-    Illuminate\Support\HigherOrderCollectionProxy::class => Tightenco\Support\HigherOrderCollectionProxy::class,
-    Illuminate\Support\HigherOrderTapProxy::class => Tightenco\Support\HigherOrderTapProxy::class,
-    Illuminate\Support\HtmlString::class => Tightenco\Support\HtmlString::class,
-    Illuminate\Support\Optional::class => Tightenco\Support\Optional::class,
-    Illuminate\Support\Str::class => Tightenco\Support\Str::class,
-    Illuminate\Support\Debug\Dumper::class => Tightenco\Support\Debug\Dumper::class,
-    Illuminate\Support\Debug\HtmlDumper::class => Tightenco\Support\Debug\HtmlDumper::class,
+    /**
+     * Contracts
+     */
+    Tightenco\Contracts\Support\Arrayable::class => Illuminate\Contracts\Support\Arrayable::class,
+    Tightenco\Contracts\Support\Htmlable::class => Illuminate\Contracts\Support\Htmlable::class,
+    Tightenco\Contracts\Support\Jsonable::class => Illuminate\Contracts\Support\Jsonable::class,
+
+    /**
+     * Support
+     */
+    Tightenco\Support\Arr::class => Illuminate\Support\Arr::class,
+    Tightenco\Support\Collection::class => Illuminate\Support\Collection::class,
+    Tightenco\Support\HigherOrderCollectionProxy::class => Illuminate\Support\HigherOrderCollectionProxy::class,
+    Tightenco\Support\HtmlString::class => Illuminate\Support\HtmlString::class,
+
+    /**
+     * Support\Debug
+     */
+    Tightenco\Support\Debug\Dumper::class => Illuminate\Support\Debug\Dumper::class,
+    Tightenco\Support\Debug\HtmlDumper::class => Illuminate\Support\Debug\HtmlDumper::class,
+
+    /**
+     * Support\Traits
+     */
+    Tightenco\Support\Traits\Macroable::class => Illuminate\Support\Traits\Macroable::class,
 ];
 
-foreach ($aliases as $illuminate => $tighten) {
-    if (class_exists($illuminate) && ! interface_exists($illuminate) && ! trait_exists($illuminate)) {
-        class_alias($illuminate, $tighten);
+foreach ($aliases as $tighten => $illuminate) {
+    if (! class_exists($illuminate) && ! interface_exists($illuminate) && ! trait_exists($illuminate)) {
+        class_alias($tighten, $illuminate);
     }
 }
diff --git a/tests/Support/SupportCollectionTest.php b/tests/Support/SupportCollectionTest.php
index 2f6c949..6d741d2 100644
--- a/tests/Support/SupportCollectionTest.php
+++ b/tests/Support/SupportCollectionTest.php
@@ -973,11 +973,9 @@ public function testExcept()
 
         $this->assertEquals(['first' => 'Taylor'], $data->except(['last', 'email', 'missing'])->all());
         $this->assertEquals(['first' => 'Taylor'], $data->except('last', 'email', 'missing')->all());
-        $this->assertEquals(['first' => 'Taylor'], $data->except(collect(['last' => 'Otwell', 'email' => 'taylorotwell@gmail.com', 'missing']))->all());
 
         $this->assertEquals(['first' => 'Taylor', 'email' => 'taylorotwell@gmail.com'], $data->except(['last'])->all());
         $this->assertEquals(['first' => 'Taylor', 'email' => 'taylorotwell@gmail.com'], $data->except('last')->all());
-        $this->assertEquals(['first' => 'Taylor', 'email' => 'taylorotwell@gmail.com'], $data->except(collect(['last' => 'Otwell']))->all());
     }
 
     public function testPluckWithArrayAndObjectValues()
@@ -1601,6 +1599,48 @@ public function testGroupByClosureWhereItemsHaveMultipleGroupsPreservingKeys()
         $this->assertEquals($expected_result, $result->toArray());
     }
 
+    public function testGroupByMultiLevelAndClosurePreservingKeys()
+    {
+        $data = new Collection([
+            10 => ['user' => 1, 'skilllevel' => 1, 'roles' => ['Role_1', 'Role_3']],
+            20 => ['user' => 2, 'skilllevel' => 1, 'roles' => ['Role_1', 'Role_2']],
+            30 => ['user' => 3, 'skilllevel' => 2, 'roles' => ['Role_1']],
+            40 => ['user' => 4, 'skilllevel' => 2, 'roles' => ['Role_2']],
+        ]);
+
+        $result = $data->groupBy([
+            'skilllevel',
+            function ($item) {
+                return $item['roles'];
+            },
+        ], true);
+
+        $expected_result = [
+            1 => [
+                'Role_1' => [
+                    10 => ['user' => 1, 'skilllevel' => 1, 'roles' => ['Role_1', 'Role_3']],
+                    20 => ['user' => 2, 'skilllevel' => 1, 'roles' => ['Role_1', 'Role_2']],
+                ],
+                'Role_3' => [
+                    10 => ['user' => 1, 'skilllevel' => 1, 'roles' => ['Role_1', 'Role_3']],
+                ],
+                'Role_2' => [
+                    20 => ['user' => 2, 'skilllevel' => 1, 'roles' => ['Role_1', 'Role_2']],
+                ],
+            ],
+            2 => [
+                'Role_1' => [
+                    30 => ['user' => 3, 'skilllevel' => 2, 'roles' => ['Role_1']],
+                ],
+                'Role_2' => [
+                    40 => ['user' => 4, 'skilllevel' => 2, 'roles' => ['Role_2']],
+                ],
+            ],
+        ];
+
+        $this->assertEquals($expected_result, $result->toArray());
+    }
+
     public function testKeyByAttribute()
     {
         $data = new Collection([['rating' => 1, 'name' => '1'], ['rating' => 2, 'name' => '2'], ['rating' => 3, 'name' => '3']]);
@@ -1928,9 +1968,11 @@ public function testOnly()
         $this->assertEquals($data->all(), $data->only(null)->all());
         $this->assertEquals(['first' => 'Taylor'], $data->only(['first', 'missing'])->all());
         $this->assertEquals(['first' => 'Taylor'], $data->only('first', 'missing')->all());
+        $this->assertEquals(['first' => 'Taylor'], $data->only(collect(['first', 'missing']))->all());
 
         $this->assertEquals(['first' => 'Taylor', 'email' => 'taylorotwell@gmail.com'], $data->only(['first', 'email'])->all());
         $this->assertEquals(['first' => 'Taylor', 'email' => 'taylorotwell@gmail.com'], $data->only('first', 'email')->all());
+        $this->assertEquals(['first' => 'Taylor', 'email' => 'taylorotwell@gmail.com'], $data->only(collect(['first', 'email']))->all());
     }
 
     public function testGettingAvgItemsFromCollection()
@@ -2422,6 +2464,12 @@ public function testUnlessDefault()
 
         $this->assertSame(['michael', 'tom', 'taylor'], $collection->toArray());
     }
+
+    public function testGetWithNullReturnsNull()
+    {
+        $collection = new Collection([1, 2, 3]);
+        $this->assertNull($collection->get(null));
+    }
 }
 
 class TestSupportCollectionHigherOrderItem