Fixed some exceptions introduced earlier.

src/Entity/Devices/DevicePart.php

@@ -78,12 +78,12 @@ class DevicePart extends AbstractDBElement
      * @ORM\ManyToOne(targetEntity="Device", inversedBy="parts")
      * @ORM\JoinColumn(name="id_device", referencedColumnName="id")
      */
-    protected Device $device;
+    protected ?Device $device = null;
 
     /**
      * @var Part
      * @ORM\ManyToOne(targetEntity="App\Entity\Parts\Part")
      * @ORM\JoinColumn(name="id_part", referencedColumnName="id")
      */
-    protected Part $part;
+    protected ?Part $part = null;
 }

src/Entity/Parts/MeasurementUnit.php

@@ -66,7 +66,7 @@ class MeasurementUnit extends AbstractPartsContainingDBElement
      * @ORM\Column(type="string", name="unit", nullable=true)
      * @Assert\Length(max=10)
      */
-    protected string $unit;
+    protected ?string $unit = null;
 
     /**
      * @var bool Determines if the amount value associated with this unit should be treated as integer.

src/Entity/Parts/PartTraits/OrderTrait.php

@@ -85,7 +85,7 @@ trait OrderTrait
      *
      * @ColumnSecurity(prefix="order", type="object")
      */
-    protected Orderdetail $order_orderdetail;
+    protected ?Orderdetail $order_orderdetail = null;
 
     /**
      * Get the selected order orderdetails of this part.

src/Entity/PriceInformations/Currency.php

@@ -78,7 +78,7 @@ class Currency extends AbstractStructuralDBElement
      * @ORM\Column(type="string")
      * @Assert\Currency()
      */
-    protected string $iso_code;
+    protected string $iso_code = "";
 
     /**
      * @ORM\OneToMany(targetEntity="Currency", mappedBy="parent", cascade={"persist"})