Fixed some inspection issues.

src/Entity/Parts/MeasurementUnit.php

@@ -119,7 +119,7 @@ class MeasurementUnit extends AbstractPartsContainingDBElement
     }
 
     /**
-     * @param string $unit
+     * @param  string|null  $unit
      *
      * @return MeasurementUnit
      */

src/Entity/Parts/PartLot.php

@@ -197,7 +197,7 @@ class PartLot extends AbstractDBElement implements TimeStampableInterface, Named
     /**
      * Sets the expiration date for the part lot. Set to null, if the part lot does not expires.
      *
-     * @param DateTime $expiration_date
+     * @param  DateTime|null  $expiration_date
      *
      * @return PartLot
      */

src/Entity/Parts/PartTraits/BasicPropertyTrait.php

@@ -166,7 +166,7 @@ trait BasicPropertyTrait
     /**
      * Sets the description of this part.
      *
-     * @param string $new_description the new description
+     * @param  string|null  $new_description  the new description
      *
      * @return $this
      */
@@ -195,7 +195,7 @@ trait BasicPropertyTrait
      * Set the category of this Part.
      * The category property is required for every part, so you can not pass null like the other properties (footprints).
      *
-     * @param Category $category The new category of this part
+     * @param  Category|null  $category  The new category of this part
      *
      * @return $this
      */