diff --git a/Controller/Controller.php b/Controller/Controller.php
index 33c15cd..86e0b0a 100644
--- a/Controller/Controller.php
+++ b/Controller/Controller.php
@@ -66,7 +66,7 @@ class Controller extends ModuleAbstract implements WebInterface
      * @var string[]
      * @since 1.0.0
      */
-    protected static $providing = [];
+    protected static array $providing = [];
 
     /**
      * Dependencies.
@@ -74,5 +74,5 @@ class Controller extends ModuleAbstract implements WebInterface
      * @var string[]
      * @since 1.0.0
      */
-    protected static $dependencies = [];
+    protected static array $dependencies = [];
 }
diff --git a/Models/Calendar.php b/Models/Calendar.php
index 7c6d9c2..06db5dd 100644
--- a/Models/Calendar.php
+++ b/Models/Calendar.php
@@ -54,7 +54,7 @@ class Calendar
     /**
      * Created at.
      *
-     * @var \DateTime
+     * @var null|\DateTime
      * @since 1.0.0
      */
     private $createdAt = null;
@@ -62,7 +62,7 @@ class Calendar
     /**
      * Current date of the calendar.
      *
-     * @var \DateTime
+     * @var null|\DateTime
      * @since 1.0.0
      */
     private $date = null;
diff --git a/Models/CalendarMapper.php b/Models/CalendarMapper.php
index 186b9bb..5e471ac 100644
--- a/Models/CalendarMapper.php
+++ b/Models/CalendarMapper.php
@@ -41,7 +41,7 @@ final class CalendarMapper extends DataMapperAbstract
      * @var array<string, array<string, bool|string>>
      * @since 1.0.0
      */
-    protected static $columns = [
+    protected static array $columns = [
         'calendar_id'          => ['name' => 'calendar_id', 'type' => 'int', 'internal' => 'id'],
         'calendar_name'        => ['name' => 'calendar_name', 'type' => 'string', 'internal' => 'name'],
         'calendar_description' => ['name' => 'calendar_description', 'type' => 'string', 'internal' => 'description'],
@@ -54,7 +54,7 @@ final class CalendarMapper extends DataMapperAbstract
      * @var array<string, array<string, null|string>>
      * @since 1.0.0
      */
-    protected static $hasMany = [
+    protected static array $hasMany = [
         'events' => [
             'mapper' => EventMapper::class,
             'table'  => 'calendar_event',
@@ -69,7 +69,7 @@ final class CalendarMapper extends DataMapperAbstract
      * @var string
      * @since 1.0.0
      */
-    protected static $table = 'calendar';
+    protected static string $table = 'calendar';
 
     /**
      * Created at.
@@ -77,7 +77,7 @@ final class CalendarMapper extends DataMapperAbstract
      * @var string
      * @since 1.0.0
      */
-    protected static $createdAt = 'calendar_created_at';
+    protected static string $createdAt = 'calendar_created_at';
 
     /**
      * Primary field name.
@@ -85,5 +85,5 @@ final class CalendarMapper extends DataMapperAbstract
      * @var string
      * @since 1.0.0
      */
-    protected static $primaryField = 'calendar_id';
+    protected static string $primaryField = 'calendar_id';
 }
diff --git a/Models/Event.php b/Models/Event.php
index be8cf3c..5771dba 100644
--- a/Models/Event.php
+++ b/Models/Event.php
@@ -56,7 +56,7 @@ class Event
     /**
      * Created.
      *
-     * @var \DateTime
+     * @var null|\DateTime
      * @since 1.0.0
      */
     private $createdAt = null;
diff --git a/Models/EventMapper.php b/Models/EventMapper.php
index 8731ae5..c9cae64 100644
--- a/Models/EventMapper.php
+++ b/Models/EventMapper.php
@@ -33,7 +33,7 @@ final class EventMapper extends DataMapperAbstract
      * @var array<string, array<string, bool|string>>
      * @since 1.0.0
      */
-    protected static $columns = [
+    protected static array $columns = [
         'calendar_event_id'          => ['name' => 'calendar_event_id', 'type' => 'int', 'internal' => 'id'],
         'calendar_event_name'        => ['name' => 'calendar_event_name', 'type' => 'string', 'internal' => 'name'],
         'calendar_event_description' => ['name' => 'calendar_event_description', 'type' => 'string', 'internal' => 'description'],
@@ -52,7 +52,7 @@ final class EventMapper extends DataMapperAbstract
      * @var array<string, array<string, string>>
      * @since 1.0.0
      */
-    protected static $ownsOne = [
+    protected static array $ownsOne = [
         'schedule' => [
             'mapper' => ScheduleMapper::class,
             'src'    => 'calendar_event_schedule',
@@ -65,7 +65,7 @@ final class EventMapper extends DataMapperAbstract
      * @var string
      * @since 1.0.0
      */
-    protected static $table = 'calendar_event';
+    protected static string $table = 'calendar_event';
 
     /**
      * Created at.
@@ -73,7 +73,7 @@ final class EventMapper extends DataMapperAbstract
      * @var string
      * @since 1.0.0
      */
-    protected static $createdAt = 'calendar_event_created_at';
+    protected static string $createdAt = 'calendar_event_created_at';
 
     /**
      * Primary field name.
@@ -81,5 +81,5 @@ final class EventMapper extends DataMapperAbstract
      * @var string
      * @since 1.0.0
      */
-    protected static $primaryField = 'calendar_event_id';
+    protected static string $primaryField = 'calendar_event_id';
 }
diff --git a/Models/Schedule.php b/Models/Schedule.php
index cd54bc2..0e3095f 100644
--- a/Models/Schedule.php
+++ b/Models/Schedule.php
@@ -93,7 +93,7 @@ class Schedule
     /**
      * Start.
      *
-     * @var \DateTime
+     * @var null|\DateTime
      * @since 1.0.0
      */
     private $start = null;
@@ -109,7 +109,7 @@ class Schedule
     /**
      * End.
      *
-     * @var \DateTime
+     * @var null|\DateTime
      * @since 1.0.0
      */
     private $end = null;
@@ -117,7 +117,7 @@ class Schedule
     /**
      * Created at.
      *
-     * @var \DateTime
+     * @var null|\DateTime
      * @since 1.0.0
      */
     private $createdAt = null;
diff --git a/Models/ScheduleMapper.php b/Models/ScheduleMapper.php
index ba1ed44..360d8c6 100644
--- a/Models/ScheduleMapper.php
+++ b/Models/ScheduleMapper.php
@@ -33,7 +33,7 @@ final class ScheduleMapper extends DataMapperAbstract
      * @var array<string, array<string, bool|string>>
      * @since 1.0.0
      */
-    protected static $columns = [
+    protected static array $columns = [
         'schedule_id'                     => ['name' => 'schedule_id', 'type' => 'int', 'internal' => 'id'],
         'schedule_uid'                    => ['name' => 'schedule_uid', 'type' => 'string', 'internal' => 'uid'],
         'schedule_status'                 => ['name' => 'schedule_status', 'type' => 'int', 'internal' => 'status'],
@@ -55,7 +55,7 @@ final class ScheduleMapper extends DataMapperAbstract
      * @var string
      * @since 1.0.0
      */
-    protected static $table = 'schedule';
+    protected static string $table = 'schedule';
 
     /**
      * Created at.
@@ -63,7 +63,7 @@ final class ScheduleMapper extends DataMapperAbstract
      * @var string
      * @since 1.0.0
      */
-    protected static $createdAt = 'schedule_created_at';
+    protected static string $createdAt = 'schedule_created_at';
 
     /**
      * Primary field name.
@@ -71,5 +71,5 @@ final class ScheduleMapper extends DataMapperAbstract
      * @var string
      * @since 1.0.0
      */
-    protected static $primaryField = 'schedule_id';
+    protected static string $primaryField = 'schedule_id';
 }