diff --git a/lib/Parser/MimeDir.php b/lib/Parser/MimeDir.php
index f6ffc37b..db0f8153 100644
--- a/lib/Parser/MimeDir.php
+++ b/lib/Parser/MimeDir.php
@@ -518,7 +518,7 @@ protected function readProperty($line)
      *
      * Now for the parameters
      *
-     * If delimiter is not set (null) this method will just return a string.
+     * If delimiter is not set (empty string) this method will just return a string.
      * If it's a comma or a semi-colon the string will be split on those
      * characters, and always return an array.
      *
diff --git a/lib/Property.php b/lib/Property.php
index 6219c9b6..50cda968 100644
--- a/lib/Property.php
+++ b/lib/Property.php
@@ -52,7 +52,7 @@ abstract class Property extends Node
      * In case this is a multi-value property. This string will be used as a
      * delimiter.
      *
-     * @var string|null
+     * @var string
      */
     public $delimiter = ';';
 
diff --git a/lib/Property/Binary.php b/lib/Property/Binary.php
index ec6713fd..1262dd05 100644
--- a/lib/Property/Binary.php
+++ b/lib/Property/Binary.php
@@ -24,9 +24,9 @@ class Binary extends Property
      * In case this is a multi-value property. This string will be used as a
      * delimiter.
      *
-     * @var string|null
+     * @var string
      */
-    public $delimiter = null;
+    public $delimiter = '';
 
     /**
      * Updates the current value.
diff --git a/lib/Property/FloatValue.php b/lib/Property/FloatValue.php
index 0d034696..e780ae6c 100644
--- a/lib/Property/FloatValue.php
+++ b/lib/Property/FloatValue.php
@@ -21,7 +21,7 @@ class FloatValue extends Property
      * In case this is a multi-value property. This string will be used as a
      * delimiter.
      *
-     * @var string|null
+     * @var string
      */
     public $delimiter = ';';
 
diff --git a/lib/Property/ICalendar/CalAddress.php b/lib/Property/ICalendar/CalAddress.php
index 86be66c1..2dbbc6ea 100644
--- a/lib/Property/ICalendar/CalAddress.php
+++ b/lib/Property/ICalendar/CalAddress.php
@@ -19,9 +19,9 @@ class CalAddress extends Text
      * In case this is a multi-value property. This string will be used as a
      * delimiter.
      *
-     * @var string|null
+     * @var string
      */
-    public $delimiter = null;
+    public $delimiter = '';
 
     /**
      * Returns the type of value.
diff --git a/lib/Property/ICalendar/Duration.php b/lib/Property/ICalendar/Duration.php
index 87f00816..e18fe191 100644
--- a/lib/Property/ICalendar/Duration.php
+++ b/lib/Property/ICalendar/Duration.php
@@ -22,7 +22,7 @@ class Duration extends Property
      * In case this is a multi-value property. This string will be used as a
      * delimiter.
      *
-     * @var string|null
+     * @var string
      */
     public $delimiter = ',';
 
diff --git a/lib/Property/ICalendar/Period.php b/lib/Property/ICalendar/Period.php
index eb375277..ae8a7891 100644
--- a/lib/Property/ICalendar/Period.php
+++ b/lib/Property/ICalendar/Period.php
@@ -23,7 +23,7 @@ class Period extends Property
      * In case this is a multi-value property. This string will be used as a
      * delimiter.
      *
-     * @var string|null
+     * @var string
      */
     public $delimiter = ',';
 
diff --git a/lib/Property/Time.php b/lib/Property/Time.php
index 544b5ced..1b81609a 100644
--- a/lib/Property/Time.php
+++ b/lib/Property/Time.php
@@ -19,9 +19,9 @@ class Time extends Text
      * In case this is a multi-value property. This string will be used as a
      * delimiter.
      *
-     * @var string|null
+     * @var string
      */
-    public $delimiter = null;
+    public $delimiter = '';
 
     /**
      * Returns the type of value.
diff --git a/lib/Property/Uri.php b/lib/Property/Uri.php
index 830cd3f1..1ad1fb19 100644
--- a/lib/Property/Uri.php
+++ b/lib/Property/Uri.php
@@ -20,9 +20,9 @@ class Uri extends Text
      * In case this is a multi-value property. This string will be used as a
      * delimiter.
      *
-     * @var string|null
+     * @var string
      */
-    public $delimiter = null;
+    public $delimiter = '';
 
     /**
      * Returns the type of value.
diff --git a/lib/Property/UtcOffset.php b/lib/Property/UtcOffset.php
index 248ed40e..04b88447 100644
--- a/lib/Property/UtcOffset.php
+++ b/lib/Property/UtcOffset.php
@@ -17,9 +17,9 @@ class UtcOffset extends Text
      * In case this is a multi-value property. This string will be used as a
      * delimiter.
      *
-     * @var string|null
+     * @var string
      */
-    public $delimiter = null;
+    public $delimiter = '';
 
     /**
      * Returns the type of value.
diff --git a/lib/Property/VCard/DateAndOrTime.php b/lib/Property/VCard/DateAndOrTime.php
index 09918b31..7bf79c48 100644
--- a/lib/Property/VCard/DateAndOrTime.php
+++ b/lib/Property/VCard/DateAndOrTime.php
@@ -24,9 +24,9 @@ class DateAndOrTime extends Property
     /**
      * Field separator.
      *
-     * @var string|null
+     * @var string
      */
-    public $delimiter = null;
+    public $delimiter = '';
 
     /**
      * Returns the type of value.
diff --git a/lib/Property/VCard/TimeStamp.php b/lib/Property/VCard/TimeStamp.php
index fccf2d60..da6ea3d4 100644
--- a/lib/Property/VCard/TimeStamp.php
+++ b/lib/Property/VCard/TimeStamp.php
@@ -21,9 +21,9 @@ class TimeStamp extends Text
      * In case this is a multi-value property. This string will be used as a
      * delimiter.
      *
-     * @var string|null
+     * @var string
      */
-    public $delimiter = null;
+    public $delimiter = '';
 
     /**
      * Returns the type of value.
diff --git a/lib/Recur/EventIterator.php b/lib/Recur/EventIterator.php
index 310bebe4..61f05d7d 100644
--- a/lib/Recur/EventIterator.php
+++ b/lib/Recur/EventIterator.php
@@ -198,6 +198,7 @@ public function __construct($input, $uid = null, DateTimeZone $timeZone = null)
      *
      * @return DateTimeImmutable
      */
+    #[\ReturnTypeWillChange]
     public function current()
     {
         if ($this->currentDate) {
@@ -285,6 +286,7 @@ public function getEventObject()
      *
      * @return int
      */
+    #[\ReturnTypeWillChange]
     public function key()
     {
         // The counter is always 1 ahead.
@@ -297,6 +299,7 @@ public function key()
      *
      * @return bool
      */
+    #[\ReturnTypeWillChange]
     public function valid()
     {
         if ($this->counter > Settings::$maxRecurrences && -1 !== Settings::$maxRecurrences) {
@@ -308,7 +311,10 @@ public function valid()
 
     /**
      * Sets the iterator back to the starting point.
+     *
+     * @return void
      */
+    #[\ReturnTypeWillChange]
     public function rewind()
     {
         $this->recurIterator->rewind();
@@ -331,7 +337,10 @@ public function rewind()
 
     /**
      * Advances the iterator with one step.
+     *
+     * @return void
      */
+    #[\ReturnTypeWillChange]
     public function next()
     {
         $this->currentOverriddenEvent = null;
diff --git a/lib/Recur/RDateIterator.php b/lib/Recur/RDateIterator.php
index d117e152..5d56657f 100644
--- a/lib/Recur/RDateIterator.php
+++ b/lib/Recur/RDateIterator.php
@@ -35,6 +35,7 @@ public function __construct($rrule, DateTimeInterface $start)
 
     /* Implementation of the Iterator interface {{{ */
 
+    #[\ReturnTypeWillChange]
     public function current()
     {
         if (!$this->valid()) {
@@ -49,6 +50,7 @@ public function current()
      *
      * @return int
      */
+    #[\ReturnTypeWillChange]
     public function key()
     {
         return $this->counter;
@@ -60,6 +62,7 @@ public function key()
      *
      * @return bool
      */
+    #[\ReturnTypeWillChange]
     public function valid()
     {
         return $this->counter <= count($this->dates);
@@ -67,7 +70,10 @@ public function valid()
 
     /**
      * Resets the iterator.
+     *
+     * @return void
      */
+    #[\ReturnTypeWillChange]
     public function rewind()
     {
         $this->currentDate = clone $this->startDate;
@@ -76,7 +82,10 @@ public function rewind()
 
     /**
      * Goes on to the next iteration.
+     *
+     * @return void
      */
+    #[\ReturnTypeWillChange]
     public function next()
     {
         ++$this->counter;
diff --git a/lib/Recur/RRuleIterator.php b/lib/Recur/RRuleIterator.php
index 0511f0ad..d556aa6c 100644
--- a/lib/Recur/RRuleIterator.php
+++ b/lib/Recur/RRuleIterator.php
@@ -38,6 +38,7 @@ public function __construct($rrule, DateTimeInterface $start)
 
     /* Implementation of the Iterator interface {{{ */
 
+    #[\ReturnTypeWillChange]
     public function current()
     {
         if (!$this->valid()) {
@@ -52,6 +53,7 @@ public function current()
      *
      * @return int
      */
+    #[\ReturnTypeWillChange]
     public function key()
     {
         return $this->counter;
@@ -64,6 +66,7 @@ public function key()
      *
      * @return bool
      */
+    #[\ReturnTypeWillChange]
     public function valid()
     {
         if (null === $this->currentDate) {
@@ -78,7 +81,10 @@ public function valid()
 
     /**
      * Resets the iterator.
+     *
+     * @return void
      */
+    #[\ReturnTypeWillChange]
     public function rewind()
     {
         $this->currentDate = clone $this->startDate;
@@ -87,7 +93,10 @@ public function rewind()
 
     /**
      * Goes on to the next iteration.
+     *
+     * @return void
      */
+    #[\ReturnTypeWillChange]
     public function next()
     {
         // Otherwise, we find the next event in the normal RRULE