diff --git a/src/Plugin/Field/FieldType/AddressItem.php b/src/Plugin/Field/FieldType/AddressItem.php
index c3197e0..3005c36 100644
--- a/src/Plugin/Field/FieldType/AddressItem.php
+++ b/src/Plugin/Field/FieldType/AddressItem.php
@@ -335,85 +335,85 @@ class AddressItem extends FieldItemBase implements AddressInterface {
   /**
    * {@inheritdoc}
    */
-  public function getCountryCode() {
-    return $this->country_code;
+  public function getCountryCode(): string {
+    return $this->country_code ?? '';
   }
 
   /**
    * {@inheritdoc}
    */
-  public function getAdministrativeArea() {
-    return $this->administrative_area;
+  public function getAdministrativeArea(): string {
+    return $this->administrative_area ?? '';
   }
 
   /**
    * {@inheritdoc}
    */
-  public function getLocality() {
-    return $this->locality;
+  public function getLocality(): string {
+    return $this->locality ?? '';
   }
 
   /**
    * {@inheritdoc}
    */
-  public function getDependentLocality() {
-    return $this->dependent_locality;
+  public function getDependentLocality(): string {
+    return $this->dependent_locality ?? '';
   }
 
   /**
    * {@inheritdoc}
    */
-  public function getPostalCode() {
-    return $this->postal_code;
+  public function getPostalCode(): string {
+    return $this->postal_code ?? '';
   }
 
   /**
    * {@inheritdoc}
    */
-  public function getSortingCode() {
-    return $this->sorting_code;
+  public function getSortingCode(): string {
+    return $this->sorting_code ?? '';
   }
 
   /**
    * {@inheritdoc}
    */
-  public function getAddressLine1() {
-    return $this->address_line1;
+  public function getAddressLine1(): string {
+    return $this->address_line1 ?? '';
   }
 
   /**
    * {@inheritdoc}
    */
-  public function getAddressLine2() {
-    return $this->address_line2;
+  public function getAddressLine2(): string {
+    return $this->address_line2 ?? '';
   }
 
   /**
    * {@inheritdoc}
    */
-  public function getOrganization() {
-    return $this->organization;
+  public function getOrganization(): string {
+    return $this->organization ?? '';
   }
 
   /**
    * {@inheritdoc}
    */
-  public function getGivenName() {
-    return $this->given_name;
+  public function getGivenName(): string {
+    return $this->given_name ?? '';
   }
 
   /**
    * {@inheritdoc}
    */
-  public function getAdditionalName() {
-    return $this->additional_name;
+  public function getAdditionalName(): string {
+    return $this->additional_name ?? '';
   }
 
   /**
    * {@inheritdoc}
    */
-  public function getFamilyName() {
-    return $this->family_name;
+  public function getFamilyName(): string {
+    return $this->family_name ?? '';
   }
 
 }
diff --git a/src/Plugin/Validation/Constraint/AddressFormatConstraintValidator.php b/src/Plugin/Validation/Constraint/AddressFormatConstraintValidator.php
index 7e8901c..640d626 100644
--- a/src/Plugin/Validation/Constraint/AddressFormatConstraintValidator.php
+++ b/src/Plugin/Validation/Constraint/AddressFormatConstraintValidator.php
@@ -2,12 +2,14 @@
 
 namespace Drupal\address\Plugin\Validation\Constraint;
 
+use CommerceGuys\Addressing\AddressFormat\AddressField;
 use CommerceGuys\Addressing\AddressFormat\AddressFormat;
 use CommerceGuys\Addressing\Validator\Constraints\AddressFormatConstraintValidator as ExternalValidator;
 use Drupal\address\FieldHelper;
 use Drupal\address\LabelHelper;
 use Drupal\Core\DependencyInjection\ContainerInjectionInterface;
 use Symfony\Component\DependencyInjection\ContainerInterface;
+use Symfony\Component\Validator\Constraint;
 
 /**
  * Validates the address format constraint.
@@ -27,7 +29,7 @@ class AddressFormatConstraintValidator extends ExternalValidator implements Cont
   /**
    * {@inheritdoc}
    */
-  protected function addViolation($field, $message, $invalid_value, AddressFormat $address_format) {
+  protected function addViolation(string $field, string $message, $invalid_value, AddressFormat $address_format) {
     $labels = LabelHelper::getFieldLabels($address_format);
     $label = $labels[$field];
 
diff --git a/src/Repository/AddressFormatRepository.php b/src/Repository/AddressFormatRepository.php
index 1f4abbb..d4d7aea 100644
--- a/src/Repository/AddressFormatRepository.php
+++ b/src/Repository/AddressFormatRepository.php
@@ -35,7 +35,7 @@ class AddressFormatRepository extends ExternalAddressFormatRepository {
   /**
    * {@inheritdoc}
    */
-  protected function processDefinition($countryCode, array $definition) {
+  protected function processDefinition($countryCode, array $definition): array {
     $definition = parent::processDefinition($countryCode, $definition);
     // Allow other modules to alter the address format.
     $event = new AddressFormatEvent($definition);
diff --git a/src/Repository/CountryRepository.php b/src/Repository/CountryRepository.php
index 30ae318..cc80819 100644
--- a/src/Repository/CountryRepository.php
+++ b/src/Repository/CountryRepository.php
@@ -40,7 +40,7 @@ class CountryRepository extends ExternalCountryRepository {
   /**
    * {@inheritdoc}
    */
-  protected function loadDefinitions($locale) {
+  protected function loadDefinitions($locale): array {
     if (isset($this->definitions[$locale])) {
       return $this->definitions[$locale];
     }
diff --git a/src/Repository/SubdivisionRepository.php b/src/Repository/SubdivisionRepository.php
index d63acc0..3aa8cb6 100644
--- a/src/Repository/SubdivisionRepository.php
+++ b/src/Repository/SubdivisionRepository.php
@@ -50,7 +50,7 @@ class SubdivisionRepository extends ExternalSubdivisionRepository {
   /**
    * {@inheritdoc}
    */
-  protected function loadDefinitions(array $parents) {
+  protected function loadDefinitions(array $parents): array {
     $group = $this->buildGroup($parents);
     if (isset($this->definitions[$group])) {
       return $this->definitions[$group];