diff --git a/psalm.xml.dist b/psalm.xml.dist
deleted file mode 100644
index c6df33e..0000000
--- a/psalm.xml.dist
+++ /dev/null
@@ -1,16 +0,0 @@
-<?xml version="1.0"?>
-<psalm
-    errorLevel="4"
-    findUnusedVariablesAndParams="true"
-    resolveFromConfigFile="true"
-    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-    xmlns="https://getpsalm.org/schema/config"
-    xsi:schemaLocation="https://getpsalm.org/schema/config vendor/vimeo/psalm/config.xsd"
->
-    <projectFiles>
-        <directory name="src"/>
-        <ignoreFiles>
-            <directory name="vendor"/>
-        </ignoreFiles>
-    </projectFiles>
-</psalm>
diff --git a/src/Exceptions/AccessTokenNotFoundException.php b/src/Exceptions/AccessTokenNotFoundException.php
index c545665..0251575 100644
--- a/src/Exceptions/AccessTokenNotFoundException.php
+++ b/src/Exceptions/AccessTokenNotFoundException.php
@@ -10,7 +10,7 @@
 
 class AccessTokenNotFoundException extends HttpException
 {
-    public function __construct(int $statusCode = 404, string $message = 'Access Token Not Found', Exception $previous = null, array $headers = [], ?int $code = 0)
+    public function __construct(int $statusCode = 404, string $message = 'Access Token Not Found', ?Exception $previous = null, array $headers = [], ?int $code = 0)
     {
         parent::__construct($statusCode, $message, $previous, $headers, $code);
     }
diff --git a/src/Exceptions/InvalidAccessTokenException.php b/src/Exceptions/InvalidAccessTokenException.php
index 8f528e1..90ace52 100644
--- a/src/Exceptions/InvalidAccessTokenException.php
+++ b/src/Exceptions/InvalidAccessTokenException.php
@@ -11,7 +11,7 @@
 
 class InvalidAccessTokenException extends HttpException
 {
-    public function __construct(int $statusCode = Response::HTTP_BAD_REQUEST, string $message = 'Invalid Access Token', Exception $previous = null, array $headers = [], ?int $code = 0)
+    public function __construct(int $statusCode = Response::HTTP_BAD_REQUEST, string $message = 'Invalid Access Token', ?Exception $previous = null, array $headers = [], ?int $code = 0)
     {
         parent::__construct($statusCode, $message, $previous, $headers, $code);
     }
diff --git a/src/Exceptions/InvalidDataOrSignatureForPersonDataException.php b/src/Exceptions/InvalidDataOrSignatureForPersonDataException.php
index 577c429..2a99d1e 100644
--- a/src/Exceptions/InvalidDataOrSignatureForPersonDataException.php
+++ b/src/Exceptions/InvalidDataOrSignatureForPersonDataException.php
@@ -10,7 +10,7 @@
 
 class InvalidDataOrSignatureForPersonDataException extends HttpException
 {
-    public function __construct(int $statusCode = 500, string $message = 'Invalid Data or Signature for Person Data', Exception $previous = null, array $headers = [], ?int $code = 0)
+    public function __construct(int $statusCode = 500, string $message = 'Invalid Data or Signature for Person Data', ?Exception $previous = null, array $headers = [], ?int $code = 0)
     {
         parent::__construct($statusCode, $message, $previous, $headers, $code);
     }
diff --git a/src/Exceptions/InvalidStateException.php b/src/Exceptions/InvalidStateException.php
index bbdce07..6eaee14 100644
--- a/src/Exceptions/InvalidStateException.php
+++ b/src/Exceptions/InvalidStateException.php
@@ -10,7 +10,7 @@
 
 class InvalidStateException extends HttpException
 {
-    public function __construct(int $statusCode = 404, string $message = 'Invalid State', Exception $previous = null, array $headers = [], ?int $code = 0)
+    public function __construct(int $statusCode = 404, string $message = 'Invalid State', ?Exception $previous = null, array $headers = [], ?int $code = 0)
     {
         parent::__construct($statusCode, $message, $previous, $headers, $code);
     }
diff --git a/src/Exceptions/MyinfoPersonDataNotFoundException.php b/src/Exceptions/MyinfoPersonDataNotFoundException.php
index ee4d5fe..2e35fd2 100644
--- a/src/Exceptions/MyinfoPersonDataNotFoundException.php
+++ b/src/Exceptions/MyinfoPersonDataNotFoundException.php
@@ -10,7 +10,7 @@
 
 class MyinfoPersonDataNotFoundException extends HttpException
 {
-    public function __construct(int $statusCode = 404, string $message = 'MyInfo Person Data not found', Exception $previous = null, array $headers = [], ?int $code = 0)
+    public function __construct(int $statusCode = 404, string $message = 'MyInfo Person Data not found', ?Exception $previous = null, array $headers = [], ?int $code = 0)
     {
         parent::__construct($statusCode, $message, $previous, $headers, $code);
     }
diff --git a/src/Exceptions/SubNotFoundException.php b/src/Exceptions/SubNotFoundException.php
index 5cc811a..993474a 100644
--- a/src/Exceptions/SubNotFoundException.php
+++ b/src/Exceptions/SubNotFoundException.php
@@ -10,7 +10,7 @@
 
 class SubNotFoundException extends HttpException
 {
-    public function __construct(int $statusCode = 404, string $message = 'Sub not found', Exception $previous = null, array $headers = [], ?int $code = 0)
+    public function __construct(int $statusCode = 404, string $message = 'Sub not found', ?Exception $previous = null, array $headers = [], ?int $code = 0)
     {
         parent::__construct($statusCode, $message, $previous, $headers, $code);
     }
diff --git a/src/Utils/MyinfoAvailabilityChecker.php b/src/Utils/MyinfoAvailabilityChecker.php
index cfc7ed5..77d974e 100644
--- a/src/Utils/MyinfoAvailabilityChecker.php
+++ b/src/Utils/MyinfoAvailabilityChecker.php
@@ -4,7 +4,7 @@
 
 namespace Ziming\LaravelMyinfoSg\Utils;
 
-use Illuminate\Support\Carbon;
+use Carbon\Carbon;
 
 /*
  * @internal