diff --git a/.github/user_feature_request.md b/.github/user_feature_request.md
index 6eb8ddc..c9595e8 100755
--- a/.github/user_feature_request.md
+++ b/.github/user_feature_request.md
@@ -8,11 +8,14 @@ assignees: ''
 ---
 
 # What is the feature you request
+
 * A clear and concise description of what the problem is. Ex. I'm always frustrated when [...]
 * A clear and concise description of what you want to happen.
 
 # Alternatives
+
 A clear and concise description of any alternative solutions or features you've considered.
 
 # Additional Information
+
 Add any other context or screenshots about the feature request here.
diff --git a/Admin/Installer.php b/Admin/Installer.php
index fa144ce..0ab6dde 100755
--- a/Admin/Installer.php
+++ b/Admin/Installer.php
@@ -63,7 +63,12 @@ final class Installer extends InstallerAbstract
             return;
         }
 
+        /** @var array $types */
         $types = \json_decode($fileContent, true);
+        if ($types === false) {
+            return;
+        }
+
         self::createBillTypes($app, $types, $defaultTemplate);
 
         /* Tax types */
@@ -72,7 +77,12 @@ final class Installer extends InstallerAbstract
             return;
         }
 
+        /** @var array $taxes */
         $taxes = \json_decode($fileContent, true);
+        if ($taxes === false) {
+            return;
+        }
+
         self::createTaxCombination($app, $taxes);
 
         /* Attributes */
@@ -81,7 +91,12 @@ final class Installer extends InstallerAbstract
             return;
         }
 
+        /** @var array $attributes */
         $attributes = \json_decode($fileContent, true);
+        if ($attributes === false) {
+            return;
+        }
+
         $attrTypes  = self::createBillAttributeTypes($app, $attributes);
         $attrValues = self::createBillAttributeValues($app, $attrTypes, $attributes);
     }
diff --git a/Controller/ApiBillController.php b/Controller/ApiBillController.php
index 4f9c799..3ea2e0f 100755
--- a/Controller/ApiBillController.php
+++ b/Controller/ApiBillController.php
@@ -205,7 +205,6 @@ final class ApiBillController extends Controller
         $bill->payment     = 0;
         $bill->paymentText = '';
 
-        /** @var \Modules\Billing\Modles\BillType */
         $bill->type = BillTypeMapper::get()
             ->where('name', 'sales_invoice')
             ->execute();
@@ -245,9 +244,9 @@ final class ApiBillController extends Controller
             ];
         }
 
-        $billLanguage = $validLanguages[0];
+        $billLanguage = $validLanguages[0] ?? ISO639x1Enum::_EN;
 
-        $clientBillLanguage = $client->getAttribute('bill_language')?->value->getValue();
+        $clientBillLanguage = $client->getAttribute('bill_language')?->value->valueStr;
         if (!empty($clientBillLanguage) && \in_array($clientBillLanguage, $validLanguages)) {
             $billLanguage = $clientBillLanguage;
         } else {
@@ -330,18 +329,16 @@ final class ApiBillController extends Controller
         $bill              = new Bill();
         $bill->createdBy   = new NullAccount($request->header->account);
         $bill->type        = $billType;
-        $bill->billTo      = (string) ($request->getDataString('billto')
-            ?? ($account->account->name1 . (!empty($account->account->name2)
+        $bill->billTo      = $request->getDataString('billto') ?? (
+            $account->account->name1 . (!empty($account->account->name2)
                 ? ', ' . $account->account->name2
                 : ''
-            )));
+            ));
         $bill->billAddress = (string) ($request->getDataString('billaddress') ?? $account->mainAddress->address);
         $bill->billZip     = (string) ($request->getDataString('billtopostal') ?? $account->mainAddress->postal);
         $bill->billCity    = (string) ($request->getDataString('billtocity') ?? $account->mainAddress->city);
-        $bill->billCountry = (string) (
-            $request->getDataString('billtocountry') ?? (
-                ($country = $account->mainAddress->getCountry()) ===  ISO3166TwoEnum::_XXX ? '' : $country)
-            );
+        $bill->billCountry =  $request->getDataString('billtocountry') ?? (
+                ($country = $account->mainAddress->getCountry()) ===  ISO3166TwoEnum::_XXX ? '' : $country);
         $bill->client          = !$request->hasData('client') ? null : $account;
         $bill->supplier        = !$request->hasData('supplier') ? null : $account;
         $bill->performanceDate = $request->getDataDateTime('performancedate') ?? new \DateTime('now');
@@ -933,7 +930,7 @@ final class ApiBillController extends Controller
         }
 
         $model = $response->get($request->uri->__toString())['response'];
-        $this->createModelRelation($request->header->account, $request->getData('id'), $model->getId(), BillMapper::class, 'bill_note', '', $request->getOrigin());
+        $this->createModelRelation($request->header->account, $request->getDataInt('id'), $model->getId(), BillMapper::class, 'bill_note', '', $request->getOrigin());
     }
 
     /**
diff --git a/Controller/ApiPriceController.php b/Controller/ApiPriceController.php
index 87b1193..52c10d3 100755
--- a/Controller/ApiPriceController.php
+++ b/Controller/ApiPriceController.php
@@ -84,7 +84,7 @@ final class ApiPriceController extends Controller
         $supplier = null;
 
         if ($request->hasData('price_client')) {
-            /** @var null|\Modules\ClientManagement\Models\Client $client */
+            /** @var \Modules\ClientManagement\Models\Client $client */
             $client = ClientMapper::get()
                 ->with('attributes')
                 ->with('attributes/type')
@@ -92,10 +92,10 @@ final class ApiPriceController extends Controller
                 ->where('id', (int) $request->getData('price_client'))
                 ->execute();
 
-            /** @var null|\Modules\ClientManagement\Models\Client|\Modules\SupplierManagement\Models\Supplier $account */
+            /** @var \Modules\ClientManagement\Models\Client */
             $account = $client;
         } else {
-            /** @var null|\Modules\SupplierManagement\Models\Supplier $supplier */
+            /** @var \Modules\SupplierManagement\Models\Supplier $supplier */
             $supplier = SupplierMapper::get()
                 ->with('attributes')
                 ->with('attributes/type')
@@ -103,7 +103,7 @@ final class ApiPriceController extends Controller
                 ->where('id', (int) $request->getData('price_supplier'))
                 ->execute();
 
-            /** @var null|\Modules\ClientManagement\Models\Client|\Modules\SupplierManagement\Models\Supplier $account */
+            /** @var \Modules\SupplierManagement\Models\Supplier $account */
             $account = $supplier;
         }
 
diff --git a/Controller/BackendController.php b/Controller/BackendController.php
index 3abcdd3..1121c3d 100755
--- a/Controller/BackendController.php
+++ b/Controller/BackendController.php
@@ -126,13 +126,15 @@ final class BackendController extends Controller
 
         $view->setData('bill', $bill);
 
+        /** @var \Modules\Auditor\Models\Auditor[] $logsBill */
         $logsBill = AuditMapper::getAll()
-            ->with('createdBy')
-            ->where('module', 'Billing')
-            ->where('type', StringUtils::intHash(BillMapper::class))
-            ->where('ref', $bill->getId())
-            ->execute();
+        ->with('createdBy')
+        ->where('module', 'Billing')
+        ->where('type', StringUtils::intHash(BillMapper::class))
+        ->where('ref', $bill->getId())
+        ->execute();
 
+        /** @var \Modules\Auditor\Models\Auditor[] $logsElements */
         $logsElements = AuditMapper::getAll()
             ->with('createdBy')
             ->where('module', 'Billing')
diff --git a/Models/Attribute/BillAttributeMapper.php b/Models/Attribute/BillAttributeMapper.php
index 09fd5c4..519ef42 100755
--- a/Models/Attribute/BillAttributeMapper.php
+++ b/Models/Attribute/BillAttributeMapper.php
@@ -24,6 +24,9 @@ use phpOMS\DataStorage\Database\Mapper\DataMapperFactory;
  * @license OMS License 2.0
  * @link    https://jingga.app
  * @since   1.0.0
+ *
+ * @template T of Attribute
+ * @extends DataMapperFactory<T>
  */
 final class BillAttributeMapper extends DataMapperFactory
 {
@@ -60,7 +63,7 @@ final class BillAttributeMapper extends DataMapperFactory
     /**
      * Model to use by the mapper.
      *
-     * @var class-string
+     * @var class-string<T>
      * @since 1.0.0
      */
     public const MODEL = Attribute::class;
diff --git a/Models/Attribute/BillAttributeTypeL11nMapper.php b/Models/Attribute/BillAttributeTypeL11nMapper.php
index daa4aed..f2e9761 100755
--- a/Models/Attribute/BillAttributeTypeL11nMapper.php
+++ b/Models/Attribute/BillAttributeTypeL11nMapper.php
@@ -24,6 +24,9 @@ use phpOMS\Localization\BaseStringL11n;
  * @license OMS License 2.0
  * @link    https://jingga.app
  * @since   1.0.0
+ *
+ * @template T of BaseStringL11n
+ * @extends DataMapperFactory<T>
  */
 final class BillAttributeTypeL11nMapper extends DataMapperFactory
 {
@@ -59,7 +62,7 @@ final class BillAttributeTypeL11nMapper extends DataMapperFactory
     /**
      * Model to use by the mapper.
      *
-     * @var class-string
+     * @var class-string<T>
      * @since 1.0.0
      */
     public const MODEL = BaseStringL11n::class;
diff --git a/Models/Attribute/BillAttributeTypeMapper.php b/Models/Attribute/BillAttributeTypeMapper.php
index 64761ed..a1e71fb 100755
--- a/Models/Attribute/BillAttributeTypeMapper.php
+++ b/Models/Attribute/BillAttributeTypeMapper.php
@@ -24,6 +24,9 @@ use phpOMS\DataStorage\Database\Mapper\DataMapperFactory;
  * @license OMS License 2.0
  * @link    https://jingga.app
  * @since   1.0.0
+ *
+ * @template T of AttributeType
+ * @extends DataMapperFactory<T>
  */
 final class BillAttributeTypeMapper extends DataMapperFactory
 {
@@ -68,7 +71,7 @@ final class BillAttributeTypeMapper extends DataMapperFactory
     /**
      * Model to use by the mapper.
      *
-     * @var class-string
+     * @var class-string<T>
      * @since 1.0.0
      */
     public const MODEL = AttributeType::class;
diff --git a/Models/Attribute/BillAttributeValueL11nMapper.php b/Models/Attribute/BillAttributeValueL11nMapper.php
index a0748a4..515dc7d 100755
--- a/Models/Attribute/BillAttributeValueL11nMapper.php
+++ b/Models/Attribute/BillAttributeValueL11nMapper.php
@@ -24,6 +24,9 @@ use phpOMS\Localization\BaseStringL11n;
  * @license OMS License 2.0
  * @link    https://jingga.app
  * @since   1.0.0
+ *
+ * @template T of BaseStringL11n
+ * @extends DataMapperFactory<T>
  */
 final class BillAttributeValueL11nMapper extends DataMapperFactory
 {
@@ -59,7 +62,7 @@ final class BillAttributeValueL11nMapper extends DataMapperFactory
     /**
      * Model to use by the mapper.
      *
-     * @var class-string
+     * @var class-string<T>
      * @since 1.0.0
      */
     public const MODEL = BaseStringL11n::class;
diff --git a/Models/Attribute/BillAttributeValueMapper.php b/Models/Attribute/BillAttributeValueMapper.php
index 1fe664e..1dc9a9f 100755
--- a/Models/Attribute/BillAttributeValueMapper.php
+++ b/Models/Attribute/BillAttributeValueMapper.php
@@ -24,6 +24,9 @@ use phpOMS\DataStorage\Database\Mapper\DataMapperFactory;
  * @license OMS License 2.0
  * @link    https://jingga.app
  * @since   1.0.0
+ *
+ * @template T of AttributeValue
+ * @extends DataMapperFactory<T>
  */
 final class BillAttributeValueMapper extends DataMapperFactory
 {
@@ -63,7 +66,7 @@ final class BillAttributeValueMapper extends DataMapperFactory
     /**
      * Model to use by the mapper.
      *
-     * @var class-string
+     * @var class-string<T>
      * @since 1.0.0
      */
     public const MODEL = AttributeValue::class;
diff --git a/Models/Bill.php b/Models/Bill.php
index 77fd1c8..daff05d 100755
--- a/Models/Bill.php
+++ b/Models/Bill.php
@@ -86,10 +86,10 @@ class Bill implements \JsonSerializable
     /**
      * Bill created at.
      *
-     * @var null|\DateTime
+     * @var \DateTime
      * @since 1.0.0
      */
-    public ?\DateTime $billDate = null;
+    public \DateTime $billDate;
 
     /**
      * Bill created at.
@@ -463,6 +463,7 @@ class Bill implements \JsonSerializable
         $this->netDiscount   = new Money(0);
         $this->grossDiscount = new Money(0);
 
+        $this->billDate  = new \DateTime('now');
         $this->createdAt = new \DateTimeImmutable();
         $this->createdBy = new NullAccount();
         $this->referral  = new NullAccount();
diff --git a/Models/BillElementMapper.php b/Models/BillElementMapper.php
index 6e3ab4f..0e8a691 100755
--- a/Models/BillElementMapper.php
+++ b/Models/BillElementMapper.php
@@ -23,6 +23,9 @@ use phpOMS\DataStorage\Database\Mapper\DataMapperFactory;
  * @license OMS License 2.0
  * @link    https://jingga.app
  * @since   1.0.0
+ *
+ * @template T of BillElement
+ * @extends DataMapperFactory<T>
  */
 final class BillElementMapper extends DataMapperFactory
 {
diff --git a/Models/BillMapper.php b/Models/BillMapper.php
index 55b5ef2..4bdc3c7 100755
--- a/Models/BillMapper.php
+++ b/Models/BillMapper.php
@@ -30,6 +30,9 @@ use phpOMS\DataStorage\Database\Mapper\DataMapperFactory;
  * @license OMS License 2.0
  * @link    https://jingga.app
  * @since   1.0.0
+ *
+ * @template T of Bill
+ * @extends DataMapperFactory<T>
  */
 class BillMapper extends DataMapperFactory
 {
diff --git a/Models/BillTypeL11nMapper.php b/Models/BillTypeL11nMapper.php
index b7c6b73..fda1bc2 100755
--- a/Models/BillTypeL11nMapper.php
+++ b/Models/BillTypeL11nMapper.php
@@ -24,6 +24,9 @@ use phpOMS\Localization\BaseStringL11n;
  * @license OMS License 2.0
  * @link    https://jingga.app
  * @since   1.0.0
+ *
+ * @template T of BaseStringL11n
+ * @extends DataMapperFactory<T>
  */
 final class BillTypeL11nMapper extends DataMapperFactory
 {
@@ -59,7 +62,7 @@ final class BillTypeL11nMapper extends DataMapperFactory
     /**
      * Model to use by the mapper.
      *
-     * @var class-string
+     * @var class-string<T>
      * @since 1.0.0
      */
     public const MODEL = BaseStringL11n::class;
diff --git a/Models/BillTypeMapper.php b/Models/BillTypeMapper.php
index 5735b7b..1b9d4ad 100755
--- a/Models/BillTypeMapper.php
+++ b/Models/BillTypeMapper.php
@@ -15,7 +15,6 @@ declare(strict_types=1);
 namespace Modules\Billing\Models;
 
 use Modules\Media\Models\CollectionMapper;
-use Modules\Media\Models\MediaMapper;
 use phpOMS\DataStorage\Database\Mapper\DataMapperFactory;
 
 /**
@@ -25,6 +24,9 @@ use phpOMS\DataStorage\Database\Mapper\DataMapperFactory;
  * @license OMS License 2.0
  * @link    https://jingga.app
  * @since   1.0.0
+ *
+ * @template T of BillType
+ * @extends DataMapperFactory<T>
  */
 final class BillTypeMapper extends DataMapperFactory
 {
@@ -97,7 +99,7 @@ final class BillTypeMapper extends DataMapperFactory
     /**
      * Model to use by the mapper.
      *
-     * @var class-string
+     * @var class-string<T>
      * @since 1.0.0
      */
     public const MODEL = BillType::class;
diff --git a/Models/Price/PriceMapper.php b/Models/Price/PriceMapper.php
index a9ebd83..bda26bc 100755
--- a/Models/Price/PriceMapper.php
+++ b/Models/Price/PriceMapper.php
@@ -14,9 +14,9 @@ declare(strict_types=1);
 
 namespace Modules\Billing\Models\Price;
 
+use Modules\Attribute\Models\AttributeValueMapper;
 use Modules\ClientManagement\Models\ClientAttributeValueMapper;
 use Modules\ClientManagement\Models\ClientMapper;
-use Modules\Attribute\Models\AttributeValueMapper;
 use Modules\ItemManagement\Models\ItemMapper;
 use Modules\SupplierManagement\Models\SupplierMapper;
 use phpOMS\DataStorage\Database\Mapper\DataMapperFactory;
@@ -29,6 +29,9 @@ use phpOMS\Localization\Defaults\CountryMapper;
  * @license OMS License 2.0
  * @link    https://jingga.app
  * @since   1.0.0
+ *
+ * @template T of Price
+ * @extends DataMapperFactory<T>
  */
 final class PriceMapper extends DataMapperFactory
 {
@@ -131,7 +134,7 @@ final class PriceMapper extends DataMapperFactory
         /**
      * Model to use by the mapper.
      *
-     * @var class-string
+     * @var class-string<T>
      * @since 1.0.0
      */
     public const MODEL = Price::class;
diff --git a/Models/PurchaseBillMapper.php b/Models/PurchaseBillMapper.php
index 28cda96..9c6ac7a 100755
--- a/Models/PurchaseBillMapper.php
+++ b/Models/PurchaseBillMapper.php
@@ -32,7 +32,7 @@ final class PurchaseBillMapper extends BillMapper
     /**
      * Model to use by the mapper.
      *
-     * @var class-string
+     * @var class-string<T>
      * @since 1.0.0
      */
     public const MODEL = Bill::class;
diff --git a/Models/SalesBillMapper.php b/Models/SalesBillMapper.php
index bdd9bb4..3dc464e 100755
--- a/Models/SalesBillMapper.php
+++ b/Models/SalesBillMapper.php
@@ -32,7 +32,7 @@ final class SalesBillMapper extends BillMapper
     /**
      * Model to use by the mapper.
      *
-     * @var class-string
+     * @var class-string<T>
      * @since 1.0.0
      */
     public const MODEL = Bill::class;
diff --git a/Models/StockBillMapper.php b/Models/StockBillMapper.php
index 1e50e47..b9ec218 100755
--- a/Models/StockBillMapper.php
+++ b/Models/StockBillMapper.php
@@ -29,7 +29,7 @@ final class StockBillMapper extends BillMapper
     /**
      * Model to use by the mapper.
      *
-     * @var class-string
+     * @var class-string<T>
      * @since 1.0.0
      */
     public const MODEL = Bill::class;
diff --git a/Models/Tax/TaxCombinationMapper.php b/Models/Tax/TaxCombinationMapper.php
index dbf1c99..8494057 100755
--- a/Models/Tax/TaxCombinationMapper.php
+++ b/Models/Tax/TaxCombinationMapper.php
@@ -14,8 +14,8 @@ declare(strict_types=1);
 
 namespace Modules\Billing\Models\Tax;
 
-use Modules\ClientManagement\Models\ClientAttributeValueMapper;
 use Modules\Attribute\Models\AttributeValueMapper;
+use Modules\ClientManagement\Models\ClientAttributeValueMapper;
 use Modules\SupplierManagement\Models\SupplierAttributeValueMapper;
 use phpOMS\DataStorage\Database\Mapper\DataMapperFactory;
 
@@ -26,6 +26,9 @@ use phpOMS\DataStorage\Database\Mapper\DataMapperFactory;
  * @license OMS License 2.0
  * @link    https://jingga.app
  * @since   1.0.0
+ *
+ * @template T of TaxCombination
+ * @extends DataMapperFactory<T>
  */
 final class TaxCombinationMapper extends DataMapperFactory
 {
@@ -75,7 +78,7 @@ final class TaxCombinationMapper extends DataMapperFactory
     /**
      * Model to use by the mapper.
      *
-     * @var class-string
+     * @var class-string<T>
      * @since 1.0.0
      */
     public const MODEL = TaxCombination::class;