diff --git a/composer.json b/composer.json
index 64e7b5d..2a778b5 100644
--- a/composer.json
+++ b/composer.json
@@ -20,8 +20,8 @@
     "require-dev": {
         "laravel/pint": "^1.2",
         "phpunit/phpunit": "^11.0",
-        "phpstan/phpstan": "^1.6",
-        "rector/rector": "^1"
+        "phpstan/phpstan": "^2.0",
+        "rector/rector": "^2.0"
     },
     "autoload": {
         "psr-4": {
diff --git a/src/Arr.php b/src/Arr.php
index 01fc73c..edf70fe 100755
--- a/src/Arr.php
+++ b/src/Arr.php
@@ -22,13 +22,9 @@ final class Arr implements Iterator, ArrayAccess, Countable
 {
     use Calculable;
 
-    /** @var array<int|string, mixed> */
-    private array $arr;
-
     /** @param array<int|string, mixed> $arr */
-    public function __construct(array $arr = [])
+    public function __construct(private array $arr = [])
     {
-        $this->arr = $arr;
     }
 
     public static function fromFunction(callable $callable, int $count): Arr
@@ -111,7 +107,7 @@ public function arr(): array
      *
      * @param non-empty-string $charNestedKey
      */
-    public function get(mixed $key, mixed $defaultValue = null, string $charNestedKey = "."): mixed
+    public function get(int|string $key, mixed $defaultValue = null, string $charNestedKey = "."): mixed
     {
         if (is_string($key)) {
             $keyString = strval($key);
@@ -137,7 +133,7 @@ public function get(mixed $key, mixed $defaultValue = null, string $charNestedKe
      * In the case the $key doesn't exist, an empty Arr can be returned
      * @param non-empty-string $charNestedKey
      */
-    public function getArr(mixed $key, mixed $defaultValue = null, string $charNestedKey = "."): Arr
+    public function getArr(int|string $key, mixed $defaultValue = null, string $charNestedKey = "."): Arr
     {
         $value = $this->getArrNullable($key, $defaultValue, $charNestedKey);
         if (is_null($value)) {
@@ -152,7 +148,7 @@ public function getArr(mixed $key, mixed $defaultValue = null, string $charNeste
      * In the case the $key doesn't exist, null can be returned
      * @param non-empty-string $charNestedKey
      */
-    public function getArrNullable(mixed $key, mixed $defaultValue = null, string $charNestedKey = "."): Arr|null
+    public function getArrNullable(int|string $key, mixed $defaultValue = null, string $charNestedKey = "."): Arr|null
     {
         $value = $this->get($key, $defaultValue, $charNestedKey);
         if (is_null($value)) {
@@ -195,7 +191,10 @@ public function set(int|string $key, mixed $value, string $charNestedKey = "."):
                 $array = &$array[$key];
             }
 
-            $array[array_shift($keys)] = $value;
+            $lastKey = array_shift($keys);
+            if ($lastKey !== null) {
+                $array[$lastKey] = $value;
+            }
             return;
 
         }
@@ -205,7 +204,7 @@ public function set(int|string $key, mixed $value, string $charNestedKey = "."):
     /**
      * Unset an array element by their key if it exists
      */
-    public function unset(mixed $key): bool
+    public function unset(int|string $key): bool
     {
         if ($this->get($key)) {
             unset($this->arr[$key]);
@@ -315,9 +314,9 @@ public function forEach(callable $callback): self
      * It returns Arr or [] depending on $returnArrClass value
      *
      * @param bool $returnArrClass true if you need Arr object
-     * @return int|string|array<int|string, mixed>|Arr
+     * @return array<int|string, mixed>|Arr
      */
-    public function keys(bool $returnArrClass = false): int|string|array|Arr
+    public function keys(bool $returnArrClass = false): array|Arr
     {
         if ($returnArrClass) {
             return self::make(array_keys($this->arr));
@@ -504,8 +503,6 @@ public function some(callable $callback): bool
     /**
      * Determines whether the array includes a certain value $element among its entries,
      * returning true or false as appropriate
-     *
-     * @param  int|null  $fromIndex
      */
     public function includes(mixed $element, ?int $fromIndex = null): bool
     {
@@ -767,7 +764,6 @@ public function find(callable $callback): mixed
      * The copyWithin() method shallow copies part of an array to another
      * location in the same array and returns it without modifying its length.
      *
-     * @param int|null $end
      * @return array<int|string, mixed>
      */
     public function copyWithin(int $target, int $start = 0, ?int $end = null): array
@@ -775,7 +771,7 @@ public function copyWithin(int $target, int $start = 0, ?int $end = null): array
         $arrayLength = $this->length();
         $chuck = $this->slice($start, $end);
         if ($target < 0) {
-            $target = $arrayLength - (int) abs($target);
+            $target = $arrayLength - abs($target);
         }
 
         foreach ($chuck as $value) {
diff --git a/src/Table.php b/src/Table.php
index c07eb1d..8eea019 100644
--- a/src/Table.php
+++ b/src/Table.php
@@ -177,13 +177,17 @@ public function groupBy(string|int $field): Table
         foreach ($this->rows as $value) {
             $property = $value->get($field);
             $property = $this->castVariableForStrval($property);
-            if (!$property) {
+            if ($property === null) {
                 continue;
             }
-            if (array_key_exists(strval($property), $result)) {
+            if ($property === false) {
                 continue;
             }
-            $result[$property] = $value;
+            $key = is_bool($property) || is_float($property) ? strval($property) : $property;
+            if (array_key_exists(strval($key), $result)) {
+                continue;
+            }
+            $result[$key] = $value;
         }
 
         return self::make(array_values($result));
diff --git a/tests/ArrSetTest.php b/tests/ArrSetTest.php
index 7054c98..f24cd05 100644
--- a/tests/ArrSetTest.php
+++ b/tests/ArrSetTest.php
@@ -32,20 +32,6 @@ public function test_basic_set(): void
     public function test_nested_set_array(): void
     {
         $articleText = "Some words as a sample sentence";
-        $textFieldArray = [
-            "type" => "doc",
-            "content" => [
-                [
-                    "content" => [
-                        [
-                            "text" => $articleText,
-                            "type" => "text"
-                        ]
-                    ],
-                    "type" => "paragraph"
-                ]
-            ]
-        ];
         $textField = Arr::make();
         $textField->set("type", "doc");
         $textField->set("content.0.content.0.text", $articleText);