diff --git a/src/Collection/Complex/TaxNumber.php b/src/Collection/Complex/TaxNumber.php
index 1bc23f8..7323efe 100644
--- a/src/Collection/Complex/TaxNumber.php
+++ b/src/Collection/Complex/TaxNumber.php
@@ -49,7 +49,7 @@ class TaxNumber extends ValueObject
      * @param  string  $number
      * @param  string|null  $prefix
      */
-    public function __construct(string $number, string $prefix = null)
+    public function __construct(string $number, ?string $prefix = null)
     {
         if (isset($this->number)) {
             throw new InvalidArgumentException(static::IMMUTABLE_MESSAGE);
diff --git a/src/Collection/Complex/Uuid.php b/src/Collection/Complex/Uuid.php
index 0c54a71..482fd73 100644
--- a/src/Collection/Complex/Uuid.php
+++ b/src/Collection/Complex/Uuid.php
@@ -48,7 +48,7 @@ class Uuid extends ValueObject
      * @param  string  $value
      * @param  string|null  $name
      */
-    public function __construct(string $value, string $name = null)
+    public function __construct(string $value, ?string $name = null)
     {
         if (isset($this->value)) {
             throw new InvalidArgumentException(static::IMMUTABLE_MESSAGE);
diff --git a/tests/Unit/Complex/TaxNumberTest.php b/tests/Unit/Complex/TaxNumberTest.php
index 4275640..88fd202 100644
--- a/tests/Unit/Complex/TaxNumberTest.php
+++ b/tests/Unit/Complex/TaxNumberTest.php
@@ -190,7 +190,7 @@
 
 class TestTaxNumber extends TaxNumber
 {
-    public function __construct(string $number, string $prefix = null)
+    public function __construct(string $number, ?string $prefix = null)
     {
         $this->number = $number;
         $this->prefix = $prefix;