diff --git a/src/EasyStatement.php b/src/EasyStatement.php
index a276284..7263075 100644
--- a/src/EasyStatement.php
+++ b/src/EasyStatement.php
@@ -420,7 +420,7 @@ public function __toString(): string
      * EasyStatement constructor.
      * @param EasyStatement|null $parent
      */
-    protected function __construct(EasyStatement $parent = null)
+    protected function __construct(?EasyStatement $parent = null)
     {
         $this->parent = $parent;
     }
diff --git a/src/Exception/MustBeArrayOrEasyStatement.php b/src/Exception/MustBeArrayOrEasyStatement.php
index 936b6cd..1c6ad2c 100644
--- a/src/Exception/MustBeArrayOrEasyStatement.php
+++ b/src/Exception/MustBeArrayOrEasyStatement.php
@@ -4,6 +4,7 @@
 
 use ParagonIE\Corner\CornerInterface;
 use ParagonIE\Corner\CornerTrait;
+use Throwable;
 
 /**
  * Class MustBeArrayOrEasyStatement
@@ -13,7 +14,7 @@ class MustBeArrayOrEasyStatement extends EasyDBException
 {
     use CornerTrait;
 
-    public function __construct(string $message = "", int $code = 0, \Throwable $previous = null)
+    public function __construct(string $message = "", int $code = 0, ?Throwable $previous = null)
     {
         parent::__construct($message, $code, $previous);
         $this->supportLink = 'https://github.com/paragonie/easydb';
diff --git a/src/Exception/MustBeEmpty.php b/src/Exception/MustBeEmpty.php
index 1293cbb..542c9cb 100644
--- a/src/Exception/MustBeEmpty.php
+++ b/src/Exception/MustBeEmpty.php
@@ -4,12 +4,13 @@
 
 use ParagonIE\Corner\CornerInterface;
 use ParagonIE\Corner\CornerTrait;
+use Throwable;
 
 class MustBeEmpty extends EasyDBException
 {
     use CornerTrait;
 
-    public function __construct(string $message = "", int $code = 0, \Throwable $previous = null)
+    public function __construct(string $message = "", int $code = 0, ?Throwable $previous = null)
     {
         parent::__construct($message, $code, $previous);
         $this->supportLink = 'https://github.com/paragonie/easydb';
diff --git a/src/Exception/MustBeNonEmpty.php b/src/Exception/MustBeNonEmpty.php
index a8cd6d5..564acde 100644
--- a/src/Exception/MustBeNonEmpty.php
+++ b/src/Exception/MustBeNonEmpty.php
@@ -4,6 +4,7 @@
 
 use ParagonIE\Corner\CornerInterface;
 use ParagonIE\Corner\CornerTrait;
+use Throwable;
 
 /**
  * Class MustBeNonEmpty
@@ -13,7 +14,7 @@ class MustBeNonEmpty extends EasyDBException
 {
     use CornerTrait;
 
-    public function __construct(string $message = "", int $code = 0, \Throwable $previous = null)
+    public function __construct(string $message = "", int $code = 0, ?Throwable $previous = null)
     {
         parent::__construct($message, $code, $previous);
         $this->supportLink = 'https://github.com/paragonie/easydb';
@@ -29,7 +30,5 @@ public function __construct(string $message = "", int $code = 0, \Throwable $pre
 Note that an empty IN statement yields an empty result. If you want it to fail
 open (a.k.a. discard the IN() statement entirely), you'll need to implement
 your own application logic to handle this behavior.";
-
-
     }
 }
diff --git a/src/Exception/MustBeOneDimensionalArray.php b/src/Exception/MustBeOneDimensionalArray.php
index 0b42c9a..d8066b3 100644
--- a/src/Exception/MustBeOneDimensionalArray.php
+++ b/src/Exception/MustBeOneDimensionalArray.php
@@ -14,7 +14,7 @@ class MustBeOneDimensionalArray extends EasyDBException
 {
     use CornerTrait;
 
-    public function __construct(string $message = "", int $code = 0, Throwable $previous = null)
+    public function __construct(string $message = "", int $code = 0, ?Throwable $previous = null)
     {
         parent::__construct($message, $code, $previous);
         $this->supportLink = 'https://github.com/paragonie/easydb#only-one-dimensional-arrays-are-allowed';
diff --git a/src/Factory.php b/src/Factory.php
index 7c8acf4..64c0239 100644
--- a/src/Factory.php
+++ b/src/Factory.php
@@ -35,8 +35,8 @@ abstract class Factory
      */
     public static function create(
         string $dsn,
-        string $username = null,
-        string $password = null,
+        ?string $username = null,
+        ?string $password = null,
         array $options = []
     ): EasyDB {
         return static::fromArray([$dsn, $username, $password, $options]);