diff --git a/src/Entity/Base/AttachmentsTrait.php b/src/Entity/Base/AttachmentsTrait.php
index c7dc7a18..53c1fc36 100644
--- a/src/Entity/Base/AttachmentsTrait.php
+++ b/src/Entity/Base/AttachmentsTrait.php
@@ -32,8 +32,12 @@ use Symfony\Component\Serializer\Annotation\Groups;
  *
  * Requirements:
  * - Class using this trait should have $id property (e.g., via DBElementTrait)
- * - Class may optionally have $master_picture_attachment property (via MasterAttachmentTrait)
+ * - Class using this trait should use MasterAttachmentTrait for full functionality
  * - Class should implement HasAttachmentsInterface
+ *
+ * Note: This trait has an optional dependency on MasterAttachmentTrait.
+ * If MasterAttachmentTrait is used, the removeAttachment and cloneAttachments methods
+ * will handle master picture attachment properly. Otherwise, those checks are no-ops.
  */
 trait AttachmentsTrait
 {
diff --git a/src/Entity/Base/StructuralElementTrait.php b/src/Entity/Base/StructuralElementTrait.php
index f8a2cabb..728ef09c 100644
--- a/src/Entity/Base/StructuralElementTrait.php
+++ b/src/Entity/Base/StructuralElementTrait.php
@@ -92,7 +92,7 @@ trait StructuralElementTrait
      * Alternative names (semicolon-separated) for this element, which can be used for searching (especially for info provider system)
      */
     #[ORM\Column(type: Types::TEXT, nullable: true, options: ['default' => null])]
-    private ?string $alternative_names = null;
+    private ?string $alternative_names = '';
 
     /**
      * Initialize structural element collections.
@@ -189,7 +189,7 @@ trait StructuralElementTrait
      *
      * The level of the root node is -1.
      *
-     * @return int the level of this element (zero means a most top element
+     * @return int the level of this element (zero means the topmost element
      *             [a sub element of the root node])
      */
     public function getLevel(): int
diff --git a/src/Entity/Contracts/StructuralElementInterface.php b/src/Entity/Contracts/StructuralElementInterface.php
index d4a17181..9743c9dd 100644
--- a/src/Entity/Contracts/StructuralElementInterface.php
+++ b/src/Entity/Contracts/StructuralElementInterface.php
@@ -64,7 +64,7 @@ interface StructuralElementInterface
      *
      * The level of the root node is -1.
      *
-     * @return int the level of this element (zero means a most top element)
+     * @return int the level of this element (zero means the topmost element)
      */
     public function getLevel(): int;
 }