diff --git a/src/Endpoints/SettlementCaptureEndpoint.php b/src/Endpoints/SettlementCaptureEndpoint.php
index 3e51443ef..553f7499b 100644
--- a/src/Endpoints/SettlementCaptureEndpoint.php
+++ b/src/Endpoints/SettlementCaptureEndpoint.php
@@ -36,7 +36,7 @@ protected function getResourceCollectionObject($count, $_links)
      * @return mixed
      * @throws \Mollie\Api\Exceptions\ApiException
      */
-    public function pageForId(string $settlementId, string $from = null, int $limit = null, array $parameters = [])
+    public function pageForId(string $settlementId, ?string $from = null, ?int $limit = null, array $parameters = [])
     {
         $this->parentId = $settlementId;
 
diff --git a/src/Endpoints/SettlementRefundEndpoint.php b/src/Endpoints/SettlementRefundEndpoint.php
index 4f751da79..53d36d79a 100644
--- a/src/Endpoints/SettlementRefundEndpoint.php
+++ b/src/Endpoints/SettlementRefundEndpoint.php
@@ -39,7 +39,7 @@ protected function getResourceObject()
      * @return mixed
      * @throws \Mollie\Api\Exceptions\ApiException
      */
-    public function pageForId(string $settlementId, string $from = null, int $limit = null, array $parameters = [])
+    public function pageForId(string $settlementId, ?string $from = null, ?int $limit = null, array $parameters = [])
     {
         $this->parentId = $settlementId;
 
diff --git a/src/HttpAdapter/Guzzle6And7RetryMiddlewareFactory.php b/src/HttpAdapter/Guzzle6And7RetryMiddlewareFactory.php
index b6d8cb73e..a0543e083 100644
--- a/src/HttpAdapter/Guzzle6And7RetryMiddlewareFactory.php
+++ b/src/HttpAdapter/Guzzle6And7RetryMiddlewareFactory.php
@@ -66,8 +66,8 @@ private function newRetryDecider()
         return function (
             $retries,
             Request $request,
-            Response $response = null,
-            TransferException $exception = null
+            ?Response $response = null,
+            ?TransferException $exception = null
         ) {
             if ($retries >= static::MAX_RETRIES) {
                 return false;
diff --git a/src/Resources/LazyCollection.php b/src/Resources/LazyCollection.php
index 0fc90f081..94179a653 100644
--- a/src/Resources/LazyCollection.php
+++ b/src/Resources/LazyCollection.php
@@ -76,7 +76,7 @@ public function filter(callable $callback): self
      * @param (callable(TValue, TKey): bool)|null  $callback
      * @return TValue|null
      */
-    public function first(callable $callback = null)
+    public function first(?callable $callback = null)
     {
         $iterator = $this->getIterator();
 
diff --git a/src/Resources/PaymentLink.php b/src/Resources/PaymentLink.php
index bef2c9e30..c37776a58 100644
--- a/src/Resources/PaymentLink.php
+++ b/src/Resources/PaymentLink.php
@@ -166,7 +166,7 @@ public function archive()
      * @param array $filters
      * @return mixed|\Mollie\Api\Resources\BaseCollection
      */
-    public function payments(string $from = null, int $limit = null, array $filters = [])
+    public function payments(?string $from = null, ?int $limit = null, array $filters = [])
     {
         return $this->client->paymentLinkPayments->pageFor(
             $this,
diff --git a/src/Resources/Settlement.php b/src/Resources/Settlement.php
index 54f71cd24..d3b77ddeb 100644
--- a/src/Resources/Settlement.php
+++ b/src/Resources/Settlement.php
@@ -118,7 +118,7 @@ public function isFailed()
      * @return PaymentCollection
      * @throws \Mollie\Api\Exceptions\ApiException
      */
-    public function payments(int $limit = null, array $parameters = []): PaymentCollection
+    public function payments(?int $limit = null, array $parameters = []): PaymentCollection
     {
         return $this->client->settlementPayments->pageForId(
             $this->id,
@@ -136,7 +136,7 @@ public function payments(int $limit = null, array $parameters = []): PaymentColl
      * @return RefundCollection
      * @throws ApiException
      */
-    public function refunds(int $limit = null, array $parameters = [])
+    public function refunds(?int $limit = null, array $parameters = [])
     {
         return $this->client->settlementRefunds->pageForId(
             $this->id,
@@ -154,7 +154,7 @@ public function refunds(int $limit = null, array $parameters = [])
      * @return ChargebackCollection
      * @throws ApiException
      */
-    public function chargebacks(int $limit = null, array $parameters = [])
+    public function chargebacks(?int $limit = null, array $parameters = [])
     {
         return $this->client->settlementChargebacks->pageForId(
             $this->id,
@@ -172,7 +172,7 @@ public function chargebacks(int $limit = null, array $parameters = [])
      * @return CaptureCollection
      * @throws ApiException
      */
-    public function captures(int $limit = null, array $parameters = [])
+    public function captures(?int $limit = null, array $parameters = [])
     {
         return $this->client->settlementCaptures->pageForId(
             $this->id,