diff --git a/src/Extensions/SiteTreeContentReview.php b/src/Extensions/SiteTreeContentReview.php
index 31c1005..2bf5672 100644
--- a/src/Extensions/SiteTreeContentReview.php
+++ b/src/Extensions/SiteTreeContentReview.php
@@ -132,13 +132,13 @@ class SiteTreeContentReview extends DataExtension implements PermissionProvider
                 $familyIDs = $group->collateFamilyIDs();
 
                 if (is_array($familyIDs)) {
-                    $groupIDs = array_merge($groupIDs, array_values($familyIDs));
+                    $groupIDs = array_merge($groupIDs, array_values($familyIDs ?? []));
                 }
             }
 
-            array_unique($groupIDs);
+            array_unique($groupIDs ?? []);
 
-            if (count($groupIDs)) {
+            if (count($groupIDs ?? [])) {
                 $groupMembers = DataObject::get(Member::class)
                     ->where("\"Group\".\"ID\" IN (" . implode(",", $groupIDs) . ")")
                     ->leftJoin("Group_Members", "\"Member\".\"ID\" = \"Group_Members\".\"MemberID\"")
@@ -676,7 +676,7 @@ class SiteTreeContentReview extends DataExtension implements PermissionProvider
             $runHour = Config::inst()->get(ContentReviewNotificationJob::class, "first_run_hour");
             $firstRunTime = date(
                 "Y-m-d H:i:s",
-                mktime($runHour, 0, 0, date("m"), date("d") + 1, date("y"))
+                mktime($runHour ?? 0, 0, 0, date("m"), date("d") + 1, date("y"))
             );
 
             singleton(QueuedJobService::class)->queueJob(
diff --git a/src/Jobs/ContentReviewNotificationJob.php b/src/Jobs/ContentReviewNotificationJob.php
index c04871a..3d961d0 100644
--- a/src/Jobs/ContentReviewNotificationJob.php
+++ b/src/Jobs/ContentReviewNotificationJob.php
@@ -108,7 +108,7 @@ class ContentReviewNotificationJob extends AbstractQueuedJob implements QueuedJo
         $nextRun = new ContentReviewNotificationJob();
 
         $nextRunTime = mktime(
-            Config::inst()->get(__CLASS__, 'next_run_hour'),
+            Config::inst()->get(__CLASS__, 'next_run_hour') ?? 0,
             Config::inst()->get(__CLASS__, 'next_run_minute'),
             0,
             date("m"),
diff --git a/src/Reports/PagesDueForReviewReport.php b/src/Reports/PagesDueForReviewReport.php
index cf4bfc3..8767235 100644
--- a/src/Reports/PagesDueForReviewReport.php
+++ b/src/Reports/PagesDueForReviewReport.php
@@ -77,8 +77,8 @@ class PagesDueForReviewReport extends Report
     public function columns()
     {
         $linkBase = singleton(CMSPageEditController::class)->Link("show");
-        $linkPath = parse_url($linkBase, PHP_URL_PATH);
-        $linkQuery = parse_url($linkBase, PHP_URL_QUERY);
+        $linkPath = parse_url($linkBase ?? '', PHP_URL_PATH);
+        $linkQuery = parse_url($linkBase ?? '', PHP_URL_QUERY);
 
         $fields = [
             "Title" => [
@@ -182,7 +182,7 @@ class PagesDueForReviewReport extends Report
                 // TODO Get value from DateField->dataValue() once we have access to form elements here
                 $nextReviewUnixSec = strtotime(
                     ' + 1 day',
-                    strtotime($params['ReviewDateBefore'])
+                    strtotime($params['ReviewDateBefore'] ?? '')
                 );
                 $records = $records->where(
                     sprintf(
@@ -209,7 +209,7 @@ class PagesDueForReviewReport extends Report
             $virtualPageClasses = ClassInfo::subclassesFor(VirtualPage::class);
             $records = $records->where(sprintf(
                 "\"SiteTree\".\"ClassName\" NOT IN ('%s')",
-                implode("','", array_values($virtualPageClasses))
+                implode("','", array_values($virtualPageClasses ?? []))
             ));
         }
 
diff --git a/src/Reports/PagesWithoutReviewScheduleReport.php b/src/Reports/PagesWithoutReviewScheduleReport.php
index e471d1a..e54d0aa 100644
--- a/src/Reports/PagesWithoutReviewScheduleReport.php
+++ b/src/Reports/PagesWithoutReviewScheduleReport.php
@@ -46,8 +46,8 @@ class PagesWithoutReviewScheduleReport extends Report
     public function columns()
     {
         $linkBase = singleton(CMSPageEditController::class)->Link("show");
-        $linkPath = parse_url($linkBase, PHP_URL_PATH);
-        $linkQuery = parse_url($linkBase, PHP_URL_QUERY);
+        $linkPath = parse_url($linkBase ?? '', PHP_URL_PATH);
+        $linkQuery = parse_url($linkBase ?? '', PHP_URL_QUERY);
 
         $fields = [
             "Title"             => [
@@ -123,7 +123,7 @@ class PagesWithoutReviewScheduleReport extends Report
             $virtualPageClasses = ClassInfo::subclassesFor(VirtualPage::class);
             $records = $records->where(sprintf(
                 "\"SiteTree\".\"ClassName\" NOT IN ('%s')",
-                implode("','", array_values($virtualPageClasses))
+                implode("','", array_values($virtualPageClasses ?? []))
             ));
         }