diff --git a/src/Exceptions/FileNotFoundException.php b/src/Exceptions/FileNotFoundException.php
index 84a896c5..b2dd5d5b 100644
--- a/src/Exceptions/FileNotFoundException.php
+++ b/src/Exceptions/FileNotFoundException.php
@@ -6,7 +6,7 @@
 
 class FileNotFoundException extends BaseException
 {
-    public function __construct(string $filePath = null)
+    public function __construct(?string $filePath = null)
     {
         parent::__construct("Documentation file not found {$filePath}");
     }
diff --git a/src/Exceptions/MissedProductionFilePathException.php b/src/Exceptions/MissedProductionFilePathException.php
index 651f15d7..5284e8d5 100755
--- a/src/Exceptions/MissedProductionFilePathException.php
+++ b/src/Exceptions/MissedProductionFilePathException.php
@@ -6,7 +6,7 @@
 
 class MissedProductionFilePathException extends Exception
 {
-    public function __construct($message = null, $code = 0, Exception $previous = null)
+    public function __construct($message = null, $code = 0, ?Exception $previous = null)
     {
         $message = $message ?? 'Production file path missed in config';
 
diff --git a/src/Exceptions/MissedRemoteDocumentationUrlException.php b/src/Exceptions/MissedRemoteDocumentationUrlException.php
index ce20a795..90a0d758 100644
--- a/src/Exceptions/MissedRemoteDocumentationUrlException.php
+++ b/src/Exceptions/MissedRemoteDocumentationUrlException.php
@@ -6,7 +6,7 @@
 
 class MissedRemoteDocumentationUrlException extends Exception
 {
-    public function __construct($message = null, $code = 0, Exception $previous = null)
+    public function __construct($message = null, $code = 0, ?Exception $previous = null)
     {
         $message = $message ?? 'Remote documentation url missed in config. Please set SWAGGER_REMOTE_DRIVER_URL env variable to define this one.';
 
diff --git a/src/Exceptions/SpecValidation/MissingFieldException.php b/src/Exceptions/SpecValidation/MissingFieldException.php
index fa5125b6..3ea58dbd 100644
--- a/src/Exceptions/SpecValidation/MissingFieldException.php
+++ b/src/Exceptions/SpecValidation/MissingFieldException.php
@@ -4,7 +4,7 @@
 
 class MissingFieldException extends InvalidSwaggerSpecException
 {
-    public function __construct(array $missingFields, string $parentField = null)
+    public function __construct(array $missingFields, ?string $parentField = null)
     {
         $fieldsString = implode(', ', $missingFields);