diff --git a/src/Actions/NotifyUsersWorkflowAction.php b/src/Actions/NotifyUsersWorkflowAction.php
index 08d68f6f..c56be4ad 100644
--- a/src/Actions/NotifyUsersWorkflowAction.php
+++ b/src/Actions/NotifyUsersWorkflowAction.php
@@ -206,7 +206,7 @@ public function getContextFields(DataObject $target)
      * @param Member $member An optional member to use. If null, will use the current logged in member
      * @return array
      */
-    public function getMemberFields(Member $member = null)
+    public function getMemberFields(?Member $member = null)
     {
         if (!$member) {
             $member = Security::getCurrentUser();
diff --git a/src/DataObjects/WorkflowInstance.php b/src/DataObjects/WorkflowInstance.php
index 7f300862..44702f49 100644
--- a/src/DataObjects/WorkflowInstance.php
+++ b/src/DataObjects/WorkflowInstance.php
@@ -324,7 +324,7 @@ public function getTargetDiff()
      * @param WorkflowDefinition $definition
      * @param DataObject $for
      */
-    public function beginWorkflow(WorkflowDefinition $definition, DataObject $for = null)
+    public function beginWorkflow(WorkflowDefinition $definition, ?DataObject $for = null)
     {
         if (!$this->ID) {
             $this->write();
diff --git a/src/Templates/WorkflowTemplate.php b/src/Templates/WorkflowTemplate.php
index 730f8e92..f0b8ccfb 100644
--- a/src/Templates/WorkflowTemplate.php
+++ b/src/Templates/WorkflowTemplate.php
@@ -190,7 +190,7 @@ public function createRelations($definition = null)
      * @return WorkflowAction
      * @throws Exception
      */
-    protected function createAction($name, $actionTemplate, WorkflowDefinition $definition = null)
+    protected function createAction($name, $actionTemplate, ?WorkflowDefinition $definition = null)
     {
         $type = $actionTemplate['type'];
         if (!$type || !class_exists($type ?? '')) {