diff --git a/.github/workflows/php.yml b/.github/workflows/php.yml
index a89f68c..cfc39fb 100644
--- a/.github/workflows/php.yml
+++ b/.github/workflows/php.yml
@@ -10,7 +10,7 @@ jobs:
     build:
         strategy:
             matrix:
-                php: ['8.0', '8.1']
+                php: ['8.1', '8.2', '8.3']
         runs-on: ubuntu-latest
 
         steps:
@@ -26,7 +26,7 @@ jobs:
               run: composer install --prefer-dist --no-progress
 
             - name: run code php-cs-fixer
-              run: ./tools/php-cs-fixer fix --config=.php-cs-fixer.php --dry-run
+              run: PHP_CS_FIXER_IGNORE_ENV=true ./tools/php-cs-fixer fix --config=.php-cs-fixer.php --dry-run
 
             - name: run phpstan
               run: ./tools/phpstan analyse -l 5 ./src
diff --git a/composer.json b/composer.json
index d550a82..9915c7f 100644
--- a/composer.json
+++ b/composer.json
@@ -4,7 +4,7 @@
     "type": "library",
     "require": {
         "guzzlehttp/guzzle": "^6.0|^7.0",
-        "php": "^8.0",
+        "php": "^8.1",
         "ext-simplexml": "*"
     },
     "require-dev": {
diff --git a/docker-compose.yml b/docker-compose.yml
index 8d5561b..8958c7f 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -5,8 +5,8 @@ services:
         container_name: fastbill_sdk
         image: dockware/flex:latest
         ports:
-            - "22:22"     # ssh
-            - "80:80"     # apache2
+            - "2222:22"     # ssh
+            - "8088:80"     # apache2
         volumes:
             - "sdk_volume:/var/www/html"
         networks:
@@ -14,7 +14,7 @@ services:
         environment:
             - XDEBUG_ENABLED=1
             - FILEBEAT_ENABLED=0
-            - PHP_VERSION=8.0
+            - PHP_VERSION=8.2
 
 
 ## ***********************************************************************
diff --git a/examples/contact/create.php b/examples/contact/create.php
index 5a382a2..0c53a94 100644
--- a/examples/contact/create.php
+++ b/examples/contact/create.php
@@ -11,10 +11,10 @@
 
 $customersService = new FastBillSdk\Contact\ContactService(
     $fastBillClient,
-    new \FastBillSdk\Common\XmlService(),
-    new \FastBillSdk\Contact\ContactValidator()
+    new FastBillSdk\Common\XmlService(),
+    new FastBillSdk\Contact\ContactValidator()
 );
-$contactEntity = new \FastBillSdk\Contact\ContactEntity();
+$contactEntity = new FastBillSdk\Contact\ContactEntity();
 $contactEntity->customerId = 123123123;
 $contactEntity->firstName = 'Max';
 $contactEntity->lastName = 'Mustermann';
diff --git a/examples/contact/delete.php b/examples/contact/delete.php
index 55c63e4..6d7bf22 100644
--- a/examples/contact/delete.php
+++ b/examples/contact/delete.php
@@ -11,10 +11,10 @@
 
 $customersService = new FastBillSdk\Contact\ContactService(
     $fastBillClient,
-    new \FastBillSdk\Common\XmlService(),
-    new \FastBillSdk\Contact\ContactValidator()
+    new FastBillSdk\Common\XmlService(),
+    new FastBillSdk\Contact\ContactValidator()
 );
-$contactEntity = new \FastBillSdk\Contact\ContactEntity();
+$contactEntity = new FastBillSdk\Contact\ContactEntity();
 $contactEntity->contactId = 112233;
 $result = $customersService->deleteContact($contactEntity);
 
diff --git a/examples/contact/get.php b/examples/contact/get.php
index c75356f..4896a50 100644
--- a/examples/contact/get.php
+++ b/examples/contact/get.php
@@ -11,10 +11,10 @@
 
 $customersService = new FastBillSdk\Contact\ContactService(
     $fastBillClient,
-    new \FastBillSdk\Common\XmlService(),
-    new \FastBillSdk\Contact\ContactValidator()
+    new FastBillSdk\Common\XmlService(),
+    new FastBillSdk\Contact\ContactValidator()
 );
-$customersSearchStruct = new \FastBillSdk\Contact\ContactSearchStruct();
+$customersSearchStruct = new FastBillSdk\Contact\ContactSearchStruct();
 $customersSearchStruct->setCustomerIdFilter(123123123);
 $result = $customersService->getContact($customersSearchStruct);
 
diff --git a/examples/contact/update.php b/examples/contact/update.php
index 397fc45..67557a6 100644
--- a/examples/contact/update.php
+++ b/examples/contact/update.php
@@ -11,10 +11,10 @@
 
 $customersService = new FastBillSdk\Contact\ContactService(
     $fastBillClient,
-    new \FastBillSdk\Common\XmlService(),
-    new \FastBillSdk\Contact\ContactValidator()
+    new FastBillSdk\Common\XmlService(),
+    new FastBillSdk\Contact\ContactValidator()
 );
-$contactEntity = new \FastBillSdk\Contact\ContactEntity();
+$contactEntity = new FastBillSdk\Contact\ContactEntity();
 $contactEntity->contactId = 112233;
 $contactEntity->firstName = 'Max';
 $contactEntity->lastName = 'Musterfrau';
diff --git a/examples/customer/create.php b/examples/customer/create.php
index 6d1947f..be0beb0 100644
--- a/examples/customer/create.php
+++ b/examples/customer/create.php
@@ -11,12 +11,12 @@
 
 $customersService = new FastBillSdk\Customer\CustomerService(
     $fastBillClient,
-    new \FastBillSdk\Common\XmlService(),
-    new \FastBillSdk\Customer\CustomerValidator()
+    new FastBillSdk\Common\XmlService(),
+    new FastBillSdk\Customer\CustomerValidator()
 );
 
-$customersEntity = new \FastBillSdk\Customer\CustomerEntity();
-$customersEntity->customerType = \FastBillSdk\Customer\CustomerEntity::CUSTOMER_TYPE_CONSUMER;
+$customersEntity = new FastBillSdk\Customer\CustomerEntity();
+$customersEntity->customerType = FastBillSdk\Customer\CustomerEntity::CUSTOMER_TYPE_CONSUMER;
 $customersEntity->firstName = 'FirstName';
 $customersEntity->lastName = 'LastName';
 $result = $customersService->createCustomer($customersEntity);
diff --git a/examples/customer/delete.php b/examples/customer/delete.php
index 3a4f6f4..35b06d1 100644
--- a/examples/customer/delete.php
+++ b/examples/customer/delete.php
@@ -11,11 +11,11 @@
 
 $customersService = new FastBillSdk\Customer\CustomerService(
     $fastBillClient,
-    new \FastBillSdk\Common\XmlService(),
-    new \FastBillSdk\Customer\CustomerValidator()
+    new FastBillSdk\Common\XmlService(),
+    new FastBillSdk\Customer\CustomerValidator()
 );
 
-$customersEntity = new \FastBillSdk\Customer\CustomerEntity();
+$customersEntity = new FastBillSdk\Customer\CustomerEntity();
 $customersEntity->customerId = 1111;
 $result = $customersService->deleteCustomer($customersEntity);
 
diff --git a/examples/customer/get.php b/examples/customer/get.php
index 95d3b22..3f88f66 100644
--- a/examples/customer/get.php
+++ b/examples/customer/get.php
@@ -11,10 +11,10 @@
 
 $customersService = new FastBillSdk\Customer\CustomerService(
     $fastBillClient,
-    new \FastBillSdk\Common\XmlService(),
-    new \FastBillSdk\Customer\CustomerValidator()
+    new FastBillSdk\Common\XmlService(),
+    new FastBillSdk\Customer\CustomerValidator()
 );
-$customersSearchStruct = new \FastBillSdk\Customer\CustomerSearchStruct();
+$customersSearchStruct = new FastBillSdk\Customer\CustomerSearchStruct();
 $customersSearchStruct->setCustomerIdFilter(123123123);
 $result = $customersService->getCustomer($customersSearchStruct);
 
diff --git a/examples/customer/update.php b/examples/customer/update.php
index 871d2c0..d8acec8 100644
--- a/examples/customer/update.php
+++ b/examples/customer/update.php
@@ -11,12 +11,12 @@
 
 $customersService = new FastBillSdk\Customer\CustomerService(
     $fastBillClient,
-    new \FastBillSdk\Common\XmlService(),
-    new \FastBillSdk\Customer\CustomerValidator()
+    new FastBillSdk\Common\XmlService(),
+    new FastBillSdk\Customer\CustomerValidator()
 );
 
-$customersEntity = new \FastBillSdk\Customer\CustomerEntity();
-$customersEntity->customerType = \FastBillSdk\Customer\CustomerEntity::CUSTOMER_TYPE_CONSUMER;
+$customersEntity = new FastBillSdk\Customer\CustomerEntity();
+$customersEntity->customerType = FastBillSdk\Customer\CustomerEntity::CUSTOMER_TYPE_CONSUMER;
 $customersEntity->customerId = 1111;
 $customersEntity->firstName = 'FirstName v2';
 $customersEntity->lastName = 'LastName v2';
diff --git a/examples/estimate/create.php b/examples/estimate/create.php
index 5d48ec0..d2d3a34 100644
--- a/examples/estimate/create.php
+++ b/examples/estimate/create.php
@@ -11,14 +11,14 @@
 
 $estimateService = new FastBillSdk\Estimate\EstimateService(
     $fastBillClient,
-    new \FastBillSdk\Common\XmlService(),
-    new \FastBillSdk\Estimate\EstimateValidator(
-        new \FastBillSdk\Estimate\EstimateItemValidator()
+    new FastBillSdk\Common\XmlService(),
+    new FastBillSdk\Estimate\EstimateValidator(
+        new FastBillSdk\Estimate\EstimateItemValidator()
     )
 );
-$estimateEntity = new \FastBillSdk\Estimate\EstimateEntity();
+$estimateEntity = new FastBillSdk\Estimate\EstimateEntity();
 $estimateEntity->customerId = 123123123;
-$estimateItemEntity = new \FastBillSdk\Estimate\EstimateItemEntity();
+$estimateItemEntity = new FastBillSdk\Estimate\EstimateItemEntity();
 $estimateItemEntity->description = 'FastBill SDK';
 $estimateItemEntity->unitPrice = '1337';
 $estimateItemEntity->vatPercent = '19';
diff --git a/examples/estimate/createinvoice.php b/examples/estimate/createinvoice.php
index c1d8d22..1254ce4 100644
--- a/examples/estimate/createinvoice.php
+++ b/examples/estimate/createinvoice.php
@@ -11,13 +11,13 @@
 
 $estimateService = new FastBillSdk\Estimate\EstimateService(
     $fastBillClient,
-    new \FastBillSdk\Common\XmlService(),
-    new \FastBillSdk\Estimate\EstimateValidator(
-        new \FastBillSdk\Estimate\EstimateItemValidator()
+    new FastBillSdk\Common\XmlService(),
+    new FastBillSdk\Estimate\EstimateValidator(
+        new FastBillSdk\Estimate\EstimateItemValidator()
     )
 );
 
-$estimateEntity = new \FastBillSdk\Estimate\EstimateEntity();
+$estimateEntity = new FastBillSdk\Estimate\EstimateEntity();
 $estimateEntity->estimateId = 16343450;
 $result = $estimateService->createInvoiceFromEstimate($estimateEntity);
 
diff --git a/examples/estimate/delete.php b/examples/estimate/delete.php
index 87eef32..3a9fe2a 100644
--- a/examples/estimate/delete.php
+++ b/examples/estimate/delete.php
@@ -11,12 +11,12 @@
 
 $estimateService = new FastBillSdk\Estimate\EstimateService(
     $fastBillClient,
-    new \FastBillSdk\Common\XmlService(),
-    new \FastBillSdk\Estimate\EstimateValidator(
-        new \FastBillSdk\Estimate\EstimateItemValidator()
+    new FastBillSdk\Common\XmlService(),
+    new FastBillSdk\Estimate\EstimateValidator(
+        new FastBillSdk\Estimate\EstimateItemValidator()
     )
 );
-$estimateEntity = new \FastBillSdk\Estimate\EstimateEntity();
+$estimateEntity = new FastBillSdk\Estimate\EstimateEntity();
 $estimateEntity->estimateId = '16343462';
 $result = $estimateService->deleteEstimate($estimateEntity);
 
diff --git a/examples/estimate/get.php b/examples/estimate/get.php
index c7fd0dd..b75530d 100644
--- a/examples/estimate/get.php
+++ b/examples/estimate/get.php
@@ -11,12 +11,12 @@
 
 $estimateService = new FastBillSdk\Estimate\EstimateService(
     $fastBillClient,
-    new \FastBillSdk\Common\XmlService(),
-    new \FastBillSdk\Estimate\EstimateValidator(
-        new \FastBillSdk\Estimate\EstimateItemValidator()
+    new FastBillSdk\Common\XmlService(),
+    new FastBillSdk\Estimate\EstimateValidator(
+        new FastBillSdk\Estimate\EstimateItemValidator()
     )
 );
-$estimateSearchStruct = new \FastBillSdk\Estimate\EstimateSearchStruct();
+$estimateSearchStruct = new FastBillSdk\Estimate\EstimateSearchStruct();
 $result = $estimateService->getEstimate($estimateSearchStruct);
 
 ini_set('xdebug.var_display_max_depth', '5');
diff --git a/examples/estimate/sendbyemail.php b/examples/estimate/sendbyemail.php
index 9dcdb0a..31b3e59 100644
--- a/examples/estimate/sendbyemail.php
+++ b/examples/estimate/sendbyemail.php
@@ -11,13 +11,13 @@
 
 $estimateService = new FastBillSdk\Estimate\EstimateService(
     $fastBillClient,
-    new \FastBillSdk\Common\XmlService(),
-    new \FastBillSdk\Estimate\EstimateValidator(
-        new \FastBillSdk\Estimate\EstimateItemValidator()
+    new FastBillSdk\Common\XmlService(),
+    new FastBillSdk\Estimate\EstimateValidator(
+        new FastBillSdk\Estimate\EstimateItemValidator()
     )
 );
 $estimateId = 16343450;
-$recipient = new \FastBillSdk\Common\RecipientEntity();
+$recipient = new FastBillSdk\Common\RecipientEntity();
 $recipient->setToEmailAddress('test@example.com');
 
 $subject = 'Estimate Subject';
diff --git a/examples/generator.php b/examples/generator.php
index 8b3ba36..eccdda0 100644
--- a/examples/generator.php
+++ b/examples/generator.php
@@ -29,7 +29,7 @@ function lowerCamelCase($string)
 VAT_VALUE';
 
 foreach (explode("\n", $fields) as $value) {
-    echo 'public $' . lowerCamelCase($value) . ';' . '<br /><br />';
+    echo 'public $' . lowerCamelCase($value) . ';<br /><br />';
 }
 
 echo ' const FIELD_MAPPING = [<br/>';
@@ -39,7 +39,7 @@ function lowerCamelCase($string)
 echo '];<br /><br />';
 
 echo ' const XML_FIELD_MAPPING = [<br/>';
-foreach (\FastBillSdk\Invoice\InvoiceEntity::FIELD_MAPPING as $key => $value) {
+foreach (FastBillSdk\Invoice\InvoiceEntity::FIELD_MAPPING as $key => $value) {
     echo '\'' . $value . '\' => \'' . $key . '\',<br />';
 }
 echo '];<br /><br />';
diff --git a/examples/product/create.php b/examples/product/create.php
index ca34b02..d53cefe 100644
--- a/examples/product/create.php
+++ b/examples/product/create.php
@@ -11,11 +11,11 @@
 
 $productService = new FastBillSdk\Product\ProductService(
     $fastBillClient,
-    new \FastBillSdk\Common\XmlService(),
-    new \FastBillSdk\Product\ProductValidator()
+    new FastBillSdk\Common\XmlService(),
+    new FastBillSdk\Product\ProductValidator()
 );
 
-$entity = new \FastBillSdk\Product\ProductEntity();
+$entity = new FastBillSdk\Product\ProductEntity();
 $entity->title = 'FastBill SDK';
 $entity->unitPrice = 1337;
 $entity->articleNumber = 222;
diff --git a/examples/product/delete.php b/examples/product/delete.php
index abd6b3f..bdb97c5 100644
--- a/examples/product/delete.php
+++ b/examples/product/delete.php
@@ -11,11 +11,11 @@
 
 $productService = new FastBillSdk\Product\ProductService(
     $fastBillClient,
-    new \FastBillSdk\Common\XmlService(),
-    new \FastBillSdk\Product\ProductValidator()
+    new FastBillSdk\Common\XmlService(),
+    new FastBillSdk\Product\ProductValidator()
 );
 
-$entity = new \FastBillSdk\Product\ProductEntity();
+$entity = new FastBillSdk\Product\ProductEntity();
 $entity->articleId = 3493981;
 
 $result = $productService->deleteProduct($entity);
diff --git a/examples/product/get.php b/examples/product/get.php
index a4d04d9..9155b20 100644
--- a/examples/product/get.php
+++ b/examples/product/get.php
@@ -11,11 +11,11 @@
 
 $productService = new FastBillSdk\Product\ProductService(
     $fastBillClient,
-    new \FastBillSdk\Common\XmlService(),
-    new \FastBillSdk\Product\ProductValidator()
+    new FastBillSdk\Common\XmlService(),
+    new FastBillSdk\Product\ProductValidator()
 );
 
-$result = $productService->getProducts(new \FastBillSdk\Product\ProductSearchStruct());
+$result = $productService->getProducts(new FastBillSdk\Product\ProductSearchStruct());
 
 ini_set('xdebug.var_display_max_depth', '5');
 ini_set('xdebug.var_display_max_children', '256');
diff --git a/examples/product/update.php b/examples/product/update.php
index c1c47ce..6ba520f 100644
--- a/examples/product/update.php
+++ b/examples/product/update.php
@@ -11,11 +11,11 @@
 
 $productService = new FastBillSdk\Product\ProductService(
     $fastBillClient,
-    new \FastBillSdk\Common\XmlService(),
-    new \FastBillSdk\Product\ProductValidator()
+    new FastBillSdk\Common\XmlService(),
+    new FastBillSdk\Product\ProductValidator()
 );
 
-$entity = new \FastBillSdk\Product\ProductEntity();
+$entity = new FastBillSdk\Product\ProductEntity();
 $entity->articleId = 3493981;
 $entity->articleNumber = 42;
 $entity->title = 'FastBill SDK v2';
diff --git a/examples/template.get.php b/examples/template.get.php
index b118ce0..9cf7489 100644
--- a/examples/template.get.php
+++ b/examples/template.get.php
@@ -11,7 +11,7 @@
 
 $templatesService = new FastBillSdk\Template\TemplateService(
     $fastBillClient,
-    new \FastBillSdk\Common\XmlService()
+    new FastBillSdk\Common\XmlService()
 );
 $result = $templatesService->getTemplate();
 
diff --git a/examples/worktime/create.php b/examples/worktime/create.php
index 735090d..719c0fe 100644
--- a/examples/worktime/create.php
+++ b/examples/worktime/create.php
@@ -11,11 +11,11 @@
 
 $workTimesService = new FastBillSdk\WorkTime\WorkTimeService(
     $fastBillClient,
-    new \FastBillSdk\Common\XmlService(),
-    new \FastBillSdk\WorkTime\WorkTimeValidator()
+    new FastBillSdk\Common\XmlService(),
+    new FastBillSdk\WorkTime\WorkTimeValidator()
 );
 
-$workTimeEntity = new \FastBillSdk\WorkTime\WorkTimeEntity();
+$workTimeEntity = new FastBillSdk\WorkTime\WorkTimeEntity();
 $workTimeEntity->customerId = 123;
 $workTimeEntity->projectId = 456;
 $workTimeEntity->comment = 'sdk test';
diff --git a/examples/worktime/delete.php b/examples/worktime/delete.php
index c7394b8..2ff1e37 100644
--- a/examples/worktime/delete.php
+++ b/examples/worktime/delete.php
@@ -11,11 +11,11 @@
 
 $workTimesService = new FastBillSdk\WorkTime\WorkTimeService(
     $fastBillClient,
-    new \FastBillSdk\Common\XmlService(),
-    new \FastBillSdk\WorkTime\WorkTimeValidator()
+    new FastBillSdk\Common\XmlService(),
+    new FastBillSdk\WorkTime\WorkTimeValidator()
 );
 
-$workTimeEntity = new \FastBillSdk\WorkTime\WorkTimeEntity();
+$workTimeEntity = new FastBillSdk\WorkTime\WorkTimeEntity();
 $workTimeEntity->timeId = 991936;
 
 $result = $workTimesService->deleteTime($workTimeEntity);
diff --git a/examples/worktime/get.php b/examples/worktime/get.php
index ca34029..f5dee08 100644
--- a/examples/worktime/get.php
+++ b/examples/worktime/get.php
@@ -11,10 +11,10 @@
 
 $workTimesService = new FastBillSdk\WorkTime\WorkTimeService(
     $fastBillClient,
-    new \FastBillSdk\Common\XmlService(),
-    new \FastBillSdk\WorkTime\WorkTimeValidator()
+    new FastBillSdk\Common\XmlService(),
+    new FastBillSdk\WorkTime\WorkTimeValidator()
 );
-$workTimesSearchStruct = new \FastBillSdk\WorkTime\WorkTimeSearchStruct();
+$workTimesSearchStruct = new FastBillSdk\WorkTime\WorkTimeSearchStruct();
 // $workTimesSearchStruct->setCustomerIdFilter(123123);
 $result = $workTimesService->getTime($workTimesSearchStruct);
 
diff --git a/examples/worktime/update.php b/examples/worktime/update.php
index 5cb1e6a..c195209 100644
--- a/examples/worktime/update.php
+++ b/examples/worktime/update.php
@@ -11,11 +11,11 @@
 
 $workTimesService = new FastBillSdk\WorkTime\WorkTimeService(
     $fastBillClient,
-    new \FastBillSdk\Common\XmlService(),
-    new \FastBillSdk\WorkTime\WorkTimeValidator()
+    new FastBillSdk\Common\XmlService(),
+    new FastBillSdk\WorkTime\WorkTimeValidator()
 );
 
-$workTimeEntity = new \FastBillSdk\WorkTime\WorkTimeEntity();
+$workTimeEntity = new FastBillSdk\WorkTime\WorkTimeEntity();
 $workTimeEntity->timeId = 991936;
 $workTimeEntity->customerId = 123;
 $workTimeEntity->projectId = 456;
diff --git a/phive.xml b/phive.xml
index 200b767..bf2c900 100644
--- a/phive.xml
+++ b/phive.xml
@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <phive xmlns="https://phar.io/phive">
-  <phar name="php-cs-fixer" version="^3.11.0" installed="3.11.0" location="./tools/php-cs-fixer" copy="true"/>
-  <phar name="phpstan" version="^1.8" installed="1.8.8" location="./tools/phpstan" copy="true"/>
+  <phar name="php-cs-fixer" version="^3.11.0" installed="3.49.0" location="./tools/php-cs-fixer" copy="true"/>
+  <phar name="phpstan" version="^1.8" installed="1.10.58" location="./tools/phpstan" copy="true"/>
 </phive>
diff --git a/src/Contact/ContactEntity.php b/src/Contact/ContactEntity.php
index a454253..1367eea 100644
--- a/src/Contact/ContactEntity.php
+++ b/src/Contact/ContactEntity.php
@@ -115,7 +115,7 @@ class ContactEntity
         'comment' => 'COMMENT',
     ];
 
-    public function __construct(\SimpleXMLElement $data = null)
+    public function __construct(?\SimpleXMLElement $data = null)
     {
         if ($data) {
             $this->setData($data);
diff --git a/src/Customer/CustomerEntity.php b/src/Customer/CustomerEntity.php
index e3fdf1f..fa5074f 100644
--- a/src/Customer/CustomerEntity.php
+++ b/src/Customer/CustomerEntity.php
@@ -179,7 +179,7 @@ class CustomerEntity
         'documentHistoryUrl' => 'DOCUMENT_HISTORY_URL',
     ];
 
-    public function __construct(\SimpleXMLElement $data = null)
+    public function __construct(?\SimpleXMLElement $data = null)
     {
         if ($data) {
             $this->setData($data);
diff --git a/src/Document/DocumentEntity.php b/src/Document/DocumentEntity.php
index a799449..ccf2db2 100644
--- a/src/Document/DocumentEntity.php
+++ b/src/Document/DocumentEntity.php
@@ -31,7 +31,7 @@ class DocumentEntity
         'note' => 'NOTE',
     ];
 
-    public function __construct(\SimpleXMLElement $data = null)
+    public function __construct(?\SimpleXMLElement $data = null)
     {
         if ($data) {
             $this->setData($data);
diff --git a/src/Estimate/EstimateEntity.php b/src/Estimate/EstimateEntity.php
index c1a945f..fe5a276 100644
--- a/src/Estimate/EstimateEntity.php
+++ b/src/Estimate/EstimateEntity.php
@@ -161,7 +161,7 @@ class EstimateEntity
         'documentUrl' => 'DOCUMENT_URL',
     ];
 
-    public function __construct(\SimpleXMLElement $data = null)
+    public function __construct(?\SimpleXMLElement $data = null)
     {
         if ($data) {
             $items = [];
diff --git a/src/Estimate/EstimateItemEntity.php b/src/Estimate/EstimateItemEntity.php
index 335dbfc..3470d2a 100644
--- a/src/Estimate/EstimateItemEntity.php
+++ b/src/Estimate/EstimateItemEntity.php
@@ -55,7 +55,7 @@ class EstimateItemEntity
         'sortOrder' => 'SORT_ORDER',
     ];
 
-    public function __construct(\SimpleXMLElement $data = null)
+    public function __construct(?\SimpleXMLElement $data = null)
     {
         if ($data) {
             $this->setData($data);
diff --git a/src/Estimate/EstimateService.php b/src/Estimate/EstimateService.php
index 99569b3..fe639ed 100644
--- a/src/Estimate/EstimateService.php
+++ b/src/Estimate/EstimateService.php
@@ -86,9 +86,9 @@ public function createInvoiceFromEstimate(EstimateEntity $entity): int
     public function sendEstimateByEmail(
         int $estimateId,
         RecipientEntity $recipient,
-        string $subject = null,
-        string $message = null,
-        bool $receiptConfirmation = null
+        ?string $subject = null,
+        ?string $message = null,
+        ?bool $receiptConfirmation = null
     ): string {
         $this->xmlService->setService('estimate.sendbyemail');
         $data['ESTIMATE_ID'] = $estimateId;
diff --git a/src/Estimate/EstimateVatItemEntity.php b/src/Estimate/EstimateVatItemEntity.php
index f2b2a8d..c480c2e 100644
--- a/src/Estimate/EstimateVatItemEntity.php
+++ b/src/Estimate/EstimateVatItemEntity.php
@@ -23,7 +23,7 @@ class EstimateVatItemEntity
         'vatValue' => 'VAT_VALUE',
     ];
 
-    public function __construct(\SimpleXMLElement $data = null)
+    public function __construct(?\SimpleXMLElement $data = null)
     {
         if ($data) {
             $this->setData($data);
diff --git a/src/Expense/ExpenseEntity.php b/src/Expense/ExpenseEntity.php
index 281df9b..f697f8a 100644
--- a/src/Expense/ExpenseEntity.php
+++ b/src/Expense/ExpenseEntity.php
@@ -95,7 +95,7 @@ class ExpenseEntity
         'servicePeriodEnd' => 'SERVICE_PERIOD_END',
     ];
 
-    public function __construct(\SimpleXMLElement $data = null)
+    public function __construct(?\SimpleXMLElement $data = null)
     {
         if ($data) {
             $this->setData($data);
diff --git a/src/ExpenseItem/ExpenseItemEntity.php b/src/ExpenseItem/ExpenseItemEntity.php
index f50bd42..90a50eb 100644
--- a/src/ExpenseItem/ExpenseItemEntity.php
+++ b/src/ExpenseItem/ExpenseItemEntity.php
@@ -73,7 +73,7 @@ class ExpenseItemEntity
         'sortOrder' => 'SORT_ORDER',
     ];
 
-    public function __construct(\SimpleXMLElement $data = null)
+    public function __construct(?\SimpleXMLElement $data = null)
     {
         if ($data) {
             $this->setData($data);
diff --git a/src/ExpenseItem/ExpenseVatItemEntity.php b/src/ExpenseItem/ExpenseVatItemEntity.php
index e7bf918..f411694 100644
--- a/src/ExpenseItem/ExpenseVatItemEntity.php
+++ b/src/ExpenseItem/ExpenseVatItemEntity.php
@@ -23,7 +23,7 @@ class ExpenseVatItemEntity
         'vatValue' => 'VAT_VALUE',
     ];
 
-    public function __construct(\SimpleXMLElement $data = null)
+    public function __construct(?\SimpleXMLElement $data = null)
     {
         if ($data) {
             $this->setData($data);
diff --git a/src/Invoice/InvoiceCommentEntity.php b/src/Invoice/InvoiceCommentEntity.php
index d1671ed..0d12194 100644
--- a/src/Invoice/InvoiceCommentEntity.php
+++ b/src/Invoice/InvoiceCommentEntity.php
@@ -17,7 +17,7 @@ class InvoiceCommentEntity
         'COMMENT_PUBLIC' => 'commentPublic',
     ];
 
-    public function __construct(\SimpleXMLElement $data = null)
+    public function __construct(?\SimpleXMLElement $data = null)
     {
         if ($data) {
             $this->setData($data);
diff --git a/src/Invoice/InvoiceEntity.php b/src/Invoice/InvoiceEntity.php
index 233510a..72dd1eb 100644
--- a/src/Invoice/InvoiceEntity.php
+++ b/src/Invoice/InvoiceEntity.php
@@ -128,6 +128,10 @@ class InvoiceEntity
 
     public $documentUrl;
 
+    public $startDate;
+
+    public $endDate;
+
     public const FIELD_MAPPING = [
         'INVOICE_ID' => 'invoiceId',
         'TYPE' => 'type',
@@ -183,6 +187,8 @@ class InvoiceEntity
         'PAYMENTS' => 'payments',
         'PAYMENT_INFO' => 'paymentInfo',
         'DOCUMENT_URL' => 'documentUrl',
+        'START_DATE' => 'startDate',
+        'END_DATE' => 'endDate',
     ];
 
     public const XML_FIELD_MAPPING = [
@@ -240,9 +246,11 @@ class InvoiceEntity
         'payments' => 'PAYMENTS',
         'paymentInfo' => 'PAYMENT_INFO',
         'documentUrl' => 'DOCUMENT_URL',
+        'startDate' => 'START_DATE',
+        'endDate' => 'END_DATE',
     ];
 
-    public function __construct(\SimpleXMLElement $data = null)
+    public function __construct(?\SimpleXMLElement $data = null)
     {
         if ($data) {
             $this->setData($data);
diff --git a/src/Invoice/InvoicePaymentEntity.php b/src/Invoice/InvoicePaymentEntity.php
index 83410a9..9c4a2a3 100644
--- a/src/Invoice/InvoicePaymentEntity.php
+++ b/src/Invoice/InvoicePaymentEntity.php
@@ -29,7 +29,7 @@ class InvoicePaymentEntity
         'NOTE' => 'note',
     ];
 
-    public function __construct(\SimpleXMLElement $data = null)
+    public function __construct(?\SimpleXMLElement $data = null)
     {
         if ($data) {
             $this->setData($data);
diff --git a/src/Invoice/InvoiceService.php b/src/Invoice/InvoiceService.php
index 5a3c1fd..d1e8766 100644
--- a/src/Invoice/InvoiceService.php
+++ b/src/Invoice/InvoiceService.php
@@ -131,8 +131,8 @@ public function cancelInvoice(InvoiceEntity $entity): InvoiceEntity
     public function sendByEmailInvoice(
         InvoiceEntity $entity,
         RecipientEntity $recipient,
-        string $subject = null,
-        string $message = null,
+        ?string $subject = null,
+        ?string $message = null,
         bool $receiptConfirmation = false
     ): string {
         $this->xmlService->setService('invoice.sendbyemail');
diff --git a/src/Item/ItemEntity.php b/src/Item/ItemEntity.php
index 8352ae3..a8dadae 100644
--- a/src/Item/ItemEntity.php
+++ b/src/Item/ItemEntity.php
@@ -71,7 +71,7 @@ class ItemEntity
         'sortOrder' => 'SORT_ORDER',
     ];
 
-    public function __construct(\SimpleXMLElement $data = null)
+    public function __construct(?\SimpleXMLElement $data = null)
     {
         if ($data) {
             $this->setData($data);
diff --git a/src/Item/VatItemEntity.php b/src/Item/VatItemEntity.php
index 0495d05..e460e41 100644
--- a/src/Item/VatItemEntity.php
+++ b/src/Item/VatItemEntity.php
@@ -23,7 +23,7 @@ class VatItemEntity
         'vatValue' => 'VAT_VALUE',
     ];
 
-    public function __construct(\SimpleXMLElement $data = null)
+    public function __construct(?\SimpleXMLElement $data = null)
     {
         if ($data) {
             $this->setData($data);
diff --git a/src/Product/ProductEntity.php b/src/Product/ProductEntity.php
index 1c62725..7ae2228 100644
--- a/src/Product/ProductEntity.php
+++ b/src/Product/ProductEntity.php
@@ -51,7 +51,7 @@ class ProductEntity
         'tags' => 'TAGS',
     ];
 
-    public function __construct(\SimpleXMLElement $data = null)
+    public function __construct(?\SimpleXMLElement $data = null)
     {
         if ($data) {
             $this->setData($data);
diff --git a/src/Project/ProjectEntity.php b/src/Project/ProjectEntity.php
index 06c169e..9763c31 100644
--- a/src/Project/ProjectEntity.php
+++ b/src/Project/ProjectEntity.php
@@ -55,7 +55,7 @@ class ProjectEntity
         'tasks' => 'TASKS',
     ];
 
-    public function __construct(\SimpleXMLElement $data = null)
+    public function __construct(?\SimpleXMLElement $data = null)
     {
         if ($data) {
             $this->setData($data);
diff --git a/src/RecurringInvoice/RecurringInvoiceEntity.php b/src/RecurringInvoice/RecurringInvoiceEntity.php
index 8e0b2b6..de4aacb 100644
--- a/src/RecurringInvoice/RecurringInvoiceEntity.php
+++ b/src/RecurringInvoice/RecurringInvoiceEntity.php
@@ -104,7 +104,7 @@ class RecurringInvoiceEntity
         'deleteExistingItems' => 'DELETE_EXISTING_ITEMS',
     ];
 
-    public function __construct(\SimpleXMLElement $data = null)
+    public function __construct(?\SimpleXMLElement $data = null)
     {
         if ($data) {
             $this->setData($data);
diff --git a/src/Revenue/RevenueEntity.php b/src/Revenue/RevenueEntity.php
index 72ff766..0f954cf 100644
--- a/src/Revenue/RevenueEntity.php
+++ b/src/Revenue/RevenueEntity.php
@@ -187,7 +187,7 @@ class RevenueEntity
         'documentUrl' => 'DOCUMENT_URL',
     ];
 
-    public function __construct(\SimpleXMLElement $data = null)
+    public function __construct(?\SimpleXMLElement $data = null)
     {
         if ($data) {
             $this->setData($data);
diff --git a/src/Template/TemplateEntity.php b/src/Template/TemplateEntity.php
index f9db558..260bf52 100644
--- a/src/Template/TemplateEntity.php
+++ b/src/Template/TemplateEntity.php
@@ -17,7 +17,7 @@ class TemplateEntity
         'TEMPLATE_HASH' => 'templateHash',
     ];
 
-    public function __construct(\SimpleXMLElement $data = null)
+    public function __construct(?\SimpleXMLElement $data = null)
     {
         if ($data) {
             $this->setData($data);
diff --git a/src/WorkTime/WorkTimeEntity.php b/src/WorkTime/WorkTimeEntity.php
index 6d23ac1..4ec32d2 100644
--- a/src/WorkTime/WorkTimeEntity.php
+++ b/src/WorkTime/WorkTimeEntity.php
@@ -51,7 +51,7 @@ class WorkTimeEntity
         'comment' => 'COMMENT',
     ];
 
-    public function __construct(\SimpleXMLElement $data = null)
+    public function __construct(?\SimpleXMLElement $data = null)
     {
         if ($data) {
             $this->setData($data);
diff --git a/tests/Helper/ApiDummyResponse.php b/tests/Helper/ApiDummyResponse.php
index 28099b8..74adbd6 100644
--- a/tests/Helper/ApiDummyResponse.php
+++ b/tests/Helper/ApiDummyResponse.php
@@ -3,6 +3,7 @@
 
 namespace FastBillSdkTest\Helper;
 
+use Psr\Http\Message\MessageInterface;
 use Psr\Http\Message\ResponseInterface;
 use Psr\Http\Message\StreamInterface;
 
@@ -18,60 +19,73 @@ public function __construct(string $responseXml)
         $this->responseXml = $responseXml;
     }
 
-    public function getStatusCode()
+    public function getProtocolVersion(): string
     {
+        // TODO: Implement getProtocolVersion() method.
     }
 
-    public function withStatus($code, $reasonPhrase = '')
+    public function withProtocolVersion(string $version): MessageInterface
     {
+        // TODO: Implement withProtocolVersion() method.
     }
 
-    public function getReasonPhrase()
+    public function getHeaders(): array
     {
+        // TODO: Implement getHeaders() method.
     }
 
-    public function getProtocolVersion()
+    public function hasHeader(string $name): bool
     {
+        // TODO: Implement hasHeader() method.
     }
 
-    public function withProtocolVersion($version)
+    public function getHeader(string $name): array
     {
+        // TODO: Implement getHeader() method.
     }
 
-    public function getHeaders()
+    public function getHeaderLine(string $name): string
     {
+        // TODO: Implement getHeaderLine() method.
     }
 
-    public function hasHeader($name)
+    public function withHeader(string $name, $value): MessageInterface
     {
+        // TODO: Implement withHeader() method.
     }
 
-    public function getHeader($name)
+    public function withAddedHeader(string $name, $value): MessageInterface
     {
+        // TODO: Implement withAddedHeader() method.
     }
 
-    public function getHeaderLine($name)
+    public function withoutHeader(string $name): MessageInterface
     {
+        // TODO: Implement withoutHeader() method.
     }
 
-    public function withHeader($name, $value)
+    public function getBody(): StreamInterface
     {
+        // TODO: Implement getBody() method.
     }
 
-    public function withAddedHeader($name, $value)
+    public function withBody(StreamInterface $body): MessageInterface
     {
+        // TODO: Implement withBody() method.
     }
 
-    public function withoutHeader($name)
+    public function getStatusCode(): int
     {
+        // TODO: Implement getStatusCode() method.
     }
 
-    public function getBody()
+    public function withStatus(int $code, string $reasonPhrase = ''): ResponseInterface
     {
-        return $this->responseXml;
+        // TODO: Implement withStatus() method.
     }
 
-    public function withBody(StreamInterface $body)
+    public function getReasonPhrase(): string
     {
+        return '';
     }
 }
diff --git a/tools/php-cs-fixer b/tools/php-cs-fixer
index 4ccc63b..cbbbe58 100755
Binary files a/tools/php-cs-fixer and b/tools/php-cs-fixer differ
diff --git a/tools/phpstan b/tools/phpstan
index ad73bb7..b2d1aa4 100755
Binary files a/tools/phpstan and b/tools/phpstan differ