diff --git a/modules/sms_user/src/AccountRegistration.php b/modules/sms_user/src/AccountRegistration.php
index ac39bcd..e4b3894 100644
--- a/modules/sms_user/src/AccountRegistration.php
+++ b/modules/sms_user/src/AccountRegistration.php
@@ -355,7 +355,7 @@ protected function generateUniqueUsername() {
    *
    * @param \Drupal\Core\Entity\EntityConstraintViolationListInterface $violations
    *   A violation list.
-   * @param string|NULL $incoming_form
+   * @param string|null $incoming_form
    *   Incoming form, if applicable.
    *
    * @return \Drupal\Core\Entity\EntityConstraintViolationListInterface
@@ -382,7 +382,7 @@ protected function removeAcceptableViolations(EntityConstraintViolationListInter
    * @param string $name
    *   The configuration name.
    *
-   * @return array|NULL
+   * @return array|null
    *   The values for the requested configuration.
    */
   protected function settings($name) {
diff --git a/modules/sms_user/src/ActiveHoursInterface.php b/modules/sms_user/src/ActiveHoursInterface.php
index 47ffc64..be9ae87 100644
--- a/modules/sms_user/src/ActiveHoursInterface.php
+++ b/modules/sms_user/src/ActiveHoursInterface.php
@@ -32,7 +32,7 @@ public function inHours(UserInterface $user, $now = 'now');
    *   A time or strtotime() relative string localised to the users timezone.
    *   Defaults to current time for the user.
    *
-   * @return \Drupal\sms_user\ActiveHoursDates|FALSE
+   * @return \Drupal\sms_user\ActiveHoursDates|false
    *   A date pair, or FALSE if no next date could be determined.
    */
   public function findNextTime(UserInterface $user, $now = 'now');
diff --git a/modules/sms_user/tests/src/Kernel/SmsFrameworkUserAccountRegistrationServiceTest.php b/modules/sms_user/tests/src/Kernel/SmsFrameworkUserAccountRegistrationServiceTest.php
index 91f5aa7..11d4a76 100644
--- a/modules/sms_user/tests/src/Kernel/SmsFrameworkUserAccountRegistrationServiceTest.php
+++ b/modules/sms_user/tests/src/Kernel/SmsFrameworkUserAccountRegistrationServiceTest.php
@@ -545,7 +545,7 @@ protected function countUsers() {
   /**
    * Count number of registered users.
    *
-   * @return \Drupal\user\UserInterface|NULL
+   * @return \Drupal\user\UserInterface|null
    *   Get last created user, or NULL if no users in database.
    */
   protected function getLastUser() {
diff --git a/src/Entity/PhoneNumberSettingsInterface.php b/src/Entity/PhoneNumberSettingsInterface.php
index 7e6ebfe..dec6789 100644
--- a/src/Entity/PhoneNumberSettingsInterface.php
+++ b/src/Entity/PhoneNumberSettingsInterface.php
@@ -116,7 +116,7 @@ public function setPurgeVerificationPhoneNumber($purge);
    * @param string $map
    *   ID to map field name, as found in sms.phone.*.*.fields.$map.
    *
-   * @return string|NULL
+   * @return string|null
    *   A field name, or NULL if not set.
    */
   public function getFieldName($map);
@@ -126,7 +126,7 @@ public function getFieldName($map);
    *
    * @param string $map
    *   ID to map field name, as found in sms.phone.*.*.fields.$map.
-   * @param string|NULL $field_name
+   * @param string|null $field_name
    *   A field name, or NULL to unset.
    *
    * @return $this
diff --git a/src/Entity/PhoneNumberVerificationInterface.php b/src/Entity/PhoneNumberVerificationInterface.php
index f93787b..53aee92 100644
--- a/src/Entity/PhoneNumberVerificationInterface.php
+++ b/src/Entity/PhoneNumberVerificationInterface.php
@@ -21,7 +21,7 @@ public function getCreatedTime();
   /**
    * Gets the entity for the phone number verification.
    *
-   * @return \Drupal\Core\Entity\EntityInterface|NULL
+   * @return \Drupal\Core\Entity\EntityInterface|null
    *   The entity for the phone number verification, or NULL if it is missing.
    */
   public function getEntity();
diff --git a/src/Entity/SmsMessage.php b/src/Entity/SmsMessage.php
index a3641b0..e3919a1 100644
--- a/src/Entity/SmsMessage.php
+++ b/src/Entity/SmsMessage.php
@@ -167,7 +167,7 @@ public function getSender() {
   /**
    * {@inheritdoc}
    *
-   * @param string|NULL $sender
+   * @param string|null $sender
    *   The name of the sender. Or NULL to defer to the label of the sender
    *   entity.
    *
diff --git a/src/Entity/SmsMessageInterface.php b/src/Entity/SmsMessageInterface.php
index f02d01b..e9b3240 100644
--- a/src/Entity/SmsMessageInterface.php
+++ b/src/Entity/SmsMessageInterface.php
@@ -14,7 +14,7 @@ interface SmsMessageInterface extends ContentEntityInterface, PlainSmsMessageInt
   /**
    * Gets the entity who sent the SMS message.
    *
-   * @return \Drupal\Core\Entity\EntityInterface|NULL
+   * @return \Drupal\Core\Entity\EntityInterface|null
    *   The entity who sent the SMS message, or NULL if it is missing.
    */
   public function getSenderEntity();
@@ -33,7 +33,7 @@ public function setSenderEntity(EntityInterface $entity);
   /**
    * Gets the entity who will receive the SMS message.
    *
-   * @return \Drupal\Core\Entity\EntityInterface|NULL
+   * @return \Drupal\Core\Entity\EntityInterface|null
    *   The entity who will receive the SMS message, or NULL if it is missing.
    */
   public function getRecipientEntity();
@@ -101,7 +101,7 @@ public function setSendTime($send_time);
    * This value does not indicate whether the message was sent, only that the
    * gateway accepted the request.
    *
-   * @return int|NULL
+   * @return int|null
    *   The timestamp when SMS message was processed, or NULL if not processed.
    */
   public function getProcessedTime();
diff --git a/src/Event/RecipientGatewayEvent.php b/src/Event/RecipientGatewayEvent.php
index a1caf02..68ceaeb 100644
--- a/src/Event/RecipientGatewayEvent.php
+++ b/src/Event/RecipientGatewayEvent.php
@@ -119,7 +119,7 @@ public function addGateway(SmsGatewayInterface $gateway, $priority = 0) {
    *
    * @param string $gateway_id
    *   A gateway plugin ID.
-   * @param int|NULL $priority
+   * @param int|null $priority
    *   The priority of the gateway to remove, or NULL to remove all gateways
    *   with the identifier.
    *
diff --git a/src/EventSubscriber/SmsMessageProcessor.php b/src/EventSubscriber/SmsMessageProcessor.php
index 1c2bf47..9f45ba9 100644
--- a/src/EventSubscriber/SmsMessageProcessor.php
+++ b/src/EventSubscriber/SmsMessageProcessor.php
@@ -215,7 +215,7 @@ public function ensureGateways(SmsMessageEvent $event) {
    * @param string $recipient
    *   A recipient phone number.
    *
-   * @return \Drupal\sms\Entity\SmsGatewayInterface|NULL
+   * @return \Drupal\sms\Entity\SmsGatewayInterface|null
    *   A gateway for the phone number, or NULL if there is no gateway.
    */
   protected function getGatewayForPhoneNumber($recipient) {
diff --git a/src/Message/SmsDeliveryReportInterface.php b/src/Message/SmsDeliveryReportInterface.php
index 76b861b..09df60b 100644
--- a/src/Message/SmsDeliveryReportInterface.php
+++ b/src/Message/SmsDeliveryReportInterface.php
@@ -10,7 +10,7 @@ interface SmsDeliveryReportInterface {
   /**
    * Gets the gateway tracking ID for the message.
    *
-   * @return string|NULL
+   * @return string|null
    *   The gateway tracking ID for the message, or NULL if there is no tracking
    *   ID.
    */
@@ -19,7 +19,7 @@ public function getMessageId();
   /**
    * Sets the gateway tracking ID for the message.
    *
-   * @param string|NULL $message_id
+   * @param string|null $message_id
    *   The gateway tracking ID for the message, or NULL if there is no tracking
    *   ID.
    *
@@ -50,7 +50,7 @@ public function setRecipient($recipient);
   /**
    * Gets the status of the message.
    *
-   * @return string|NULL
+   * @return string|null
    *   A status code from \Drupal\sms\Message\SmsMessageReportStatus, or NULL if
    *   unknown.
    */
@@ -59,7 +59,7 @@ public function getStatus();
   /**
    * Sets the status of the message.
    *
-   * @param string|NULL $status
+   * @param string|null $status
    *   A status code from \Drupal\sms\Message\SmsMessageReportStatus, or NULL if
    *   unknown.
    *
@@ -90,7 +90,7 @@ public function setStatusMessage($message);
   /**
    * Gets the time the message was queued.
    *
-   * @return int|NULL
+   * @return int|null
    *   The timestamp when the message was queued, or NULL if unknown.
    */
   public function getTimeQueued();
@@ -98,7 +98,7 @@ public function getTimeQueued();
   /**
    * Sets the time the message was queued.
    *
-   * @param int|NULL $time
+   * @param int|null $time
    *   The timestamp when the message was queued, or NULL if unknown.
    *
    * @return $this
@@ -109,7 +109,7 @@ public function setTimeQueued($time);
   /**
    * Gets the time the message was delivered to the recipient.
    *
-   * @return int|NULL
+   * @return int|null
    *   The timestamp when the message was delivered to the recipient, or NULL if
    *   unknown.
    */
@@ -118,7 +118,7 @@ public function getTimeDelivered();
   /**
    * Sets the time the message was delivered to the recipient.
    *
-   * @param int|NULL $time
+   * @param int|null $time
    *   The timestamp when the message was delivered to the recipient, or NULL if
    *   unknown.
    *
diff --git a/src/Message/SmsMessageInterface.php b/src/Message/SmsMessageInterface.php
index 5646e11..a15c8ec 100644
--- a/src/Message/SmsMessageInterface.php
+++ b/src/Message/SmsMessageInterface.php
@@ -64,7 +64,7 @@ public function removeRecipients(array $recipients);
   /**
    * Get the gateway for this message.
    *
-   * @return \Drupal\sms\Entity\SmsGatewayInterface|NULL
+   * @return \Drupal\sms\Entity\SmsGatewayInterface|null
    *   A gateway plugin instance, or NULL to let the provider decide.
    */
   public function getGateway();
@@ -145,7 +145,7 @@ public function removeOption($name);
   /**
    * Get the result associated with this SMS message.
    *
-   * @return \Drupal\sms\Message\SmsMessageResultInterface|NULL
+   * @return \Drupal\sms\Message\SmsMessageResultInterface|null
    *   The result associated with this SMS message, or NULL if there is no
    *   result.
    */
@@ -154,7 +154,7 @@ public function getResult();
   /**
    * Set the result associated with this SMS message.
    *
-   * @param \Drupal\sms\Message\SmsMessageResultInterface|NULL $result
+   * @param \Drupal\sms\Message\SmsMessageResultInterface|null $result
    *   The result to associate with this SMS message, or NULL if there is no
    *   result.
    *
@@ -166,7 +166,7 @@ public function setResult(SmsMessageResultInterface $result = NULL);
   /**
    * Gets the name of the sender of this SMS message.
    *
-   * @return string|NULL
+   * @return string|null
    *   The name of the sender, or NULL if none is defined.
    */
   public function getSender();
@@ -174,7 +174,7 @@ public function getSender();
   /**
    * Set the name of the sender of this SMS message.
    *
-   * @param string|NULL $sender
+   * @param string|null $sender
    *   The name of the sender.
    *
    * @return $this
@@ -231,7 +231,7 @@ public function getUuid();
   /**
    * Gets the user who created the SMS message.
    *
-   * @return int|NULL
+   * @return int|null
    *   The ID of the user who created the message. Or NULL if no user entity is
    *   associated as the sender.
    */
diff --git a/src/Message/SmsMessageResultInterface.php b/src/Message/SmsMessageResultInterface.php
index 840f286..d356ea5 100644
--- a/src/Message/SmsMessageResultInterface.php
+++ b/src/Message/SmsMessageResultInterface.php
@@ -10,7 +10,7 @@ interface SmsMessageResultInterface {
   /**
    * Gets the error of the message.
    *
-   * @return string|NULL
+   * @return string|null
    *   A error code from \Drupal\sms\Message\SmsMessageResultError, or NULL if
    *   there was no error.
    */
@@ -22,7 +22,7 @@ public function getError();
    * Usually a setting an error on a result indicates something went wrong with
    * the entire transaction.
    *
-   * @param string|NULL $error
+   * @param string|null $error
    *   A error code from \Drupal\sms\Message\SmsMessageResultError, or NULL if
    *   unknown.
    *
@@ -56,7 +56,7 @@ public function setErrorMessage($message);
    * @param string $recipient
    *   The number of the recipient for which the report is to be retrieved.
    *
-   * @return \Drupal\sms\Message\SmsDeliveryReportInterface|NULL
+   * @return \Drupal\sms\Message\SmsDeliveryReportInterface|null
    *   A delivery report object, or NULL if there is no report for the
    *   recipient.
    *
@@ -97,7 +97,7 @@ public function addReport(SmsDeliveryReportInterface $report);
   /**
    * Gets the credit balance after this transaction.
    *
-   * @return float|NULL
+   * @return float|null
    *   The credit balance after the message is processed, or NULL if unknown.
    */
   public function getCreditsBalance();
@@ -105,7 +105,7 @@ public function getCreditsBalance();
   /**
    * Sets the credit balance after this transaction.
    *
-   * @param float|NULL $balance
+   * @param float|null $balance
    *   The credit balance after the message is processed, or NULL if unknown.
    *
    * @return $this
@@ -119,7 +119,7 @@ public function setCreditsBalance($balance);
   /**
    * Gets the credits consumed for this transaction.
    *
-   * @return float|NULL
+   * @return float|null
    *   The credits consumed for this transaction, or NULL if unknown.
    */
   public function getCreditsUsed();
@@ -127,7 +127,7 @@ public function getCreditsUsed();
   /**
    * Sets the credits consumed for this transaction.
    *
-   * @param float|NULL $credits_used
+   * @param float|null $credits_used
    *   The credits consumed for this transaction, or NULL if unknown.
    *
    * @return $this
diff --git a/src/Plugin/SmsGatewayPluginInterface.php b/src/Plugin/SmsGatewayPluginInterface.php
index 585c832..5f22690 100644
--- a/src/Plugin/SmsGatewayPluginInterface.php
+++ b/src/Plugin/SmsGatewayPluginInterface.php
@@ -31,7 +31,7 @@ public function send(SmsMessageInterface $sms);
    * The 'credit_balance_available' plugin annotation should be set to inform
    * the framework whether this gateway supports balance queries.
    *
-   * @return float|NULL
+   * @return float|null
    *   The credit balance of the gateway, or NULL if unknown.
    */
   public function getCreditsBalance();
@@ -56,7 +56,7 @@ public function parseDeliveryReports(Request $request, Response $response);
   /**
    * Gets delivery reports from the gateway.
    *
-   * @param string[]|NULL $message_ids
+   * @param string[]|null $message_ids
    *   A list of specific message ID's to pull, or NULL to get any reports which
    *   have not been requested previously.
    *
diff --git a/src/Provider/PhoneNumberProviderInterface.php b/src/Provider/PhoneNumberProviderInterface.php
index 2ac6e13..48ed1f9 100644
--- a/src/Provider/PhoneNumberProviderInterface.php
+++ b/src/Provider/PhoneNumberProviderInterface.php
@@ -15,7 +15,7 @@ interface PhoneNumberProviderInterface {
    *
    * @param \Drupal\Core\Entity\EntityInterface $entity
    *   An entity to get phone numbers.
-   * @param bool|NULL $verified
+   * @param bool|null $verified
    *   Whether the returned phone numbers must be verified, or NULL to get all
    *   phone numbers regardless of status.
    *
@@ -35,7 +35,7 @@ public function getPhoneNumbers(EntityInterface $entity, $verified = TRUE);
    * @param \Drupal\sms\Message\SmsMessageInterface $sms_message
    *   The SMS message to send to the entity.
    *
-   * @return \Drupal\sms\Message\SmsMessageResultInterface|FALSE
+   * @return \Drupal\sms\Message\SmsMessageResultInterface|false
    *   The message result from the gateway.
    *
    * @throws \Drupal\sms\Exception\NoPhoneNumberException
diff --git a/src/Provider/PhoneNumberVerificationInterface.php b/src/Provider/PhoneNumberVerificationInterface.php
index bd1474d..ff5af26 100644
--- a/src/Provider/PhoneNumberVerificationInterface.php
+++ b/src/Provider/PhoneNumberVerificationInterface.php
@@ -18,7 +18,7 @@ interface PhoneNumberVerificationInterface {
    * @param string $bundle
    *   An entity bundle.
    *
-   * @return \Drupal\sms\Entity\PhoneNumberSettingsInterface|NULL
+   * @return \Drupal\sms\Entity\PhoneNumberSettingsInterface|null
    *   A phone number settings entity, or NULL if it does not exist.
    */
   public function getPhoneNumberSettings($entity_type_id, $bundle);
@@ -29,7 +29,7 @@ public function getPhoneNumberSettings($entity_type_id, $bundle);
    * @param \Drupal\Core\Entity\EntityInterface $entity
    *   The entity to get settings.
    *
-   * @return \Drupal\sms\Entity\PhoneNumberSettingsInterface|NULL
+   * @return \Drupal\sms\Entity\PhoneNumberSettingsInterface|null
    *   A phone number settings entity, or NULL if it does not exist.
    *
    * @throws \Drupal\sms\Exception\PhoneNumberSettingsException
@@ -43,7 +43,7 @@ public function getPhoneNumberSettingsForEntity(EntityInterface $entity);
    * @param string $code
    *   A string to check is a verification code.
    *
-   * @return \Drupal\sms\Entity\PhoneNumberVerificationInterface|FALSE
+   * @return \Drupal\sms\Entity\PhoneNumberVerificationInterface|false
    *   A phone number verification entity, or FALSE if $code is not a valid
    *   verification code.
    */
@@ -59,7 +59,7 @@ public function getPhoneVerificationByCode($code);
    *
    * @param string $phone_number
    *   A phone number.
-   * @param bool|NULL $verified
+   * @param bool|null $verified
    *   Whether the returned phone numbers must be verified, or NULL to get all
    *   regardless of status.
    * @param string $entity_type
@@ -78,7 +78,7 @@ public function getPhoneVerificationByPhoneNumber($phone_number, $verified = TRU
    * @param string $phone_number
    *   A phone number.
    *
-   * @return \Drupal\sms\Entity\PhoneNumberVerificationInterface|NULL
+   * @return \Drupal\sms\Entity\PhoneNumberVerificationInterface|null
    *   The phone number verification for an entity and phone number pair.
    */
   public function getPhoneVerificationByEntity(EntityInterface $entity, $phone_number);
@@ -94,7 +94,7 @@ public function getPhoneVerificationByEntity(EntityInterface $entity, $phone_num
    * @param string $phone_number
    *   A phone number.
    *
-   * @return \Drupal\sms\Entity\PhoneNumberVerificationInterface|NULL
+   * @return \Drupal\sms\Entity\PhoneNumberVerificationInterface|null
    *   A phone number verification.
    */
   public function newPhoneVerification(EntityInterface $entity, $phone_number);
diff --git a/src/Tests/SmsFrameworkPhoneNumberTest.php b/src/Tests/SmsFrameworkPhoneNumberTest.php
index c8981c5..89b5d3d 100644
--- a/src/Tests/SmsFrameworkPhoneNumberTest.php
+++ b/src/Tests/SmsFrameworkPhoneNumberTest.php
@@ -92,7 +92,7 @@ public function testPhoneNumberVerificationDeleted() {
   /**
    * Count verification codes in database.
    *
-   * @param \Drupal\Core\Entity\EntityInterface|NULL $entity
+   * @param \Drupal\Core\Entity\EntityInterface|null $entity
    *   The entity to count verification codes for, or NULL to count all codes.
    *
    * @return int
diff --git a/src/Tests/SmsFrameworkTestTrait.php b/src/Tests/SmsFrameworkTestTrait.php
index 01e8b5a..4a4e814 100644
--- a/src/Tests/SmsFrameworkTestTrait.php
+++ b/src/Tests/SmsFrameworkTestTrait.php
@@ -73,7 +73,7 @@ function getTestMessages(SmsGatewayInterface $sms_gateway) {
    * @param \Drupal\sms\Entity\SmsGatewayInterface $sms_gateway
    *   A gateway plugin.
    *
-   * @return \Drupal\sms\Message\SmsMessageInterface|FALSE
+   * @return \Drupal\sms\Message\SmsMessageInterface|false
    *   The last SMS message, or FALSE if no messages have been sent.
    */
   public function getLastTestMessage(SmsGatewayInterface $sms_gateway) {
@@ -85,7 +85,7 @@ public function getLastTestMessage(SmsGatewayInterface $sms_gateway) {
   /**
    * Resets SMS messages stored in memory by 'Memory' gateway.
    *
-   * @param \Drupal\sms\Entity\SmsGatewayInterface|NULL $sms_gateway
+   * @param \Drupal\sms\Entity\SmsGatewayInterface|null $sms_gateway
    *   A gateway plugin, or NULL to reset all messages.
    */
   public function resetTestMessages(SmsGatewayInterface $sms_gateway = NULL) {
@@ -120,7 +120,7 @@ protected function getIncomingMessages(SmsGatewayInterface $sms_gateway) {
    * @param \Drupal\sms\Entity\SmsGatewayInterface $sms_gateway
    *   A gateway plugin.
    *
-   * @return \Drupal\sms\Message\SmsMessageInterface|FALSE
+   * @return \Drupal\sms\Message\SmsMessageInterface|false
    *   The last message, or FALSE if no messages were received.
    */
   protected function getLastIncomingMessage(SmsGatewayInterface $sms_gateway) {
@@ -132,7 +132,7 @@ protected function getLastIncomingMessage(SmsGatewayInterface $sms_gateway) {
   /**
    * Resets incoming messages stored in memory by gateway.
    *
-   * @param \Drupal\sms\Entity\SmsGatewayInterface|NULL $sms_gateway
+   * @param \Drupal\sms\Entity\SmsGatewayInterface|null $sms_gateway
    *   A gateway plugin, or NULL to reset all messages.
    */
   protected function resetIncomingMessages(SmsGatewayInterface $sms_gateway = NULL) {
@@ -252,7 +252,7 @@ protected function verifyPhoneNumber(EntityInterface $entity, $phone_number) {
   /**
    * Gets the last phone number verification that was created.
    *
-   * @return \Drupal\sms\Entity\PhoneNumberVerificationInterface|FALSE
+   * @return \Drupal\sms\Entity\PhoneNumberVerificationInterface|false
    *   The last verification created, or FALSE if no verifications exist.
    */
   protected function getLastVerification() {
@@ -307,7 +307,7 @@ protected function randomSmsMessage($uid = 1) {
   /**
    * Generates random phone numbers for tests.
    *
-   * @param int|NULL $quantity
+   * @param int|null $quantity
    *   Quantity of phone numbers, or NULL to generate at least 2.
    *
    * @return array