diff --git a/src/DataTables/Column/LocaleDateTimeColumn.php b/src/DataTables/Column/LocaleDateTimeColumn.php
index f9103f86..c380bada 100644
--- a/src/DataTables/Column/LocaleDateTimeColumn.php
+++ b/src/DataTables/Column/LocaleDateTimeColumn.php
@@ -58,7 +58,7 @@ class LocaleDateTimeColumn extends AbstractColumn
 {
     /**
      * @param $value
-     * @return bool|mixed|string
+     * @return string
      * @throws Exception
      */
     public function normalize($value): string
diff --git a/src/DataTables/Column/SIUnitNumberColumn.php b/src/DataTables/Column/SIUnitNumberColumn.php
index e03cac1a..77d2a197 100644
--- a/src/DataTables/Column/SIUnitNumberColumn.php
+++ b/src/DataTables/Column/SIUnitNumberColumn.php
@@ -21,6 +21,8 @@ class SIUnitNumberColumn extends AbstractColumn
 
         $resolver->setDefault('precision', 2);
         $resolver->setDefault('unit', '');
+
+        return $this;
     }
 
     public function normalize($value)
diff --git a/src/DataTables/Column/SelectColumn.php b/src/DataTables/Column/SelectColumn.php
index a3ba9161..b4dd17e8 100644
--- a/src/DataTables/Column/SelectColumn.php
+++ b/src/DataTables/Column/SelectColumn.php
@@ -21,6 +21,8 @@ class SelectColumn extends AbstractColumn
             'className' => 'select-checkbox no-colvis',
             'visible' => true,
         ]);
+
+        return $this;
     }
 
     public function normalize($value)
diff --git a/src/DataTables/Filters/Constraints/BooleanConstraint.php b/src/DataTables/Filters/Constraints/BooleanConstraint.php
index dd2870ed..c72c7c6e 100644
--- a/src/DataTables/Filters/Constraints/BooleanConstraint.php
+++ b/src/DataTables/Filters/Constraints/BooleanConstraint.php
@@ -13,7 +13,8 @@ class BooleanConstraint extends AbstractConstraint
 
     public function __construct(string $property, string $identifier = null, ?bool $default_value = null)
     {
-        parent::__construct($property, $identifier, $default_value);
+        parent::__construct($property, $identifier);
+        $this->value = $default_value;
     }
 
     /**
diff --git a/src/DataTables/Filters/Constraints/EntityConstraint.php b/src/DataTables/Filters/Constraints/EntityConstraint.php
index 359507c0..52a1c642 100644
--- a/src/DataTables/Filters/Constraints/EntityConstraint.php
+++ b/src/DataTables/Filters/Constraints/EntityConstraint.php
@@ -8,7 +8,7 @@ use App\Services\Trees\NodesListBuilder;
 use Doctrine\ORM\QueryBuilder;
 
 /**
- * @template T
+ * @template T of AbstractDBElement
  */
 class EntityConstraint extends AbstractConstraint
 {
@@ -16,7 +16,7 @@ class EntityConstraint extends AbstractConstraint
     private const ALLOWED_OPERATOR_VALUES_STRUCTURAL = ['INCLUDING_CHILDREN', 'EXCLUDING_CHILDREN'];
 
     /**
-     * @var
+     * @var NodesListBuilder
      */
     protected $nodesListBuilder;
 
@@ -37,7 +37,7 @@ class EntityConstraint extends AbstractConstraint
 
     /**
      * @param  NodesListBuilder|null  $nodesListBuilder
-     * @param  class-string  $class
+     * @param  class-string<T>  $class
      * @param  string  $property
      * @param  string|null  $identifier
      * @param  null  $value
@@ -80,7 +80,7 @@ class EntityConstraint extends AbstractConstraint
     }
 
     /**
-     * @return mixed|null
+     * @return T|null
      */
     public function getValue(): ?AbstractDBElement
     {
diff --git a/src/Repository/AbstractPartsContainingRepository.php b/src/Repository/AbstractPartsContainingRepository.php
index adb7c828..88b9d021 100644
--- a/src/Repository/AbstractPartsContainingRepository.php
+++ b/src/Repository/AbstractPartsContainingRepository.php
@@ -33,7 +33,7 @@ abstract class AbstractPartsContainingRepository extends StructuralDBElementRepo
      * @param  object  $element  the element for which the parts should be determined
      * @param  array  $order_by  The order of the parts. Format ['name' => 'ASC']
      *
-     * @return Part
+     * @return Part[]
      */
     abstract public function getParts(object $element, array $order_by = ['name' => 'ASC']): array;
 
diff --git a/src/Services/Trees/NodesListBuilder.php b/src/Services/Trees/NodesListBuilder.php
index b2d2c159..0af0341c 100644
--- a/src/Services/Trees/NodesListBuilder.php
+++ b/src/Services/Trees/NodesListBuilder.php
@@ -92,7 +92,7 @@ class NodesListBuilder
      * Returns a flattened list of all (recursive) children elements of the given AbstractStructuralDBElement.
      * The value is cached for performance reasons.
      *
-     * @template T
+     * @template T of AbstractStructuralDBElement
      * @param  T $element
      * @return T[]
      */