diff --git a/src/Entity.php b/src/Entity.php
index 1b5d69a..5ffea2e 100644
--- a/src/Entity.php
+++ b/src/Entity.php
@@ -47,7 +47,13 @@ abstract class Entity
     {
         $url = trim($url);
         $validator = Validation::createValidator();
-        $violations = $validator->validate($url, new Assert\Url());
+        $violations = $validator->validate(
+            $url,
+            [
+                new Assert\Url(),
+                new Assert\NotBlank()
+            ]
+        );
         if ($violations->count() > 0) {
             throw new ValidationFailedException(null, $violations);
         }
@@ -73,8 +79,7 @@ abstract class Entity
                 new Assert\Regex([
                     'pattern' => $regEx,
                     'message' => 'This value does not match the regular expression "{{ pattern }}".'
-                ]),
-                new Assert\NotBlank()
+                ])
             ]
         );
         if ($violations->count() > 0) {
diff --git a/src/Entity/Set.php b/src/Entity/Set.php
index e79457c..9355035 100644
--- a/src/Entity/Set.php
+++ b/src/Entity/Set.php
@@ -54,8 +54,8 @@ class Set extends Entity
     /**
      * A description of the set.
      */
-    #[ORM\Column(type: 'text')]
-    private string $description = '';
+    #[ORM\Column(type: 'text', nullable: true)]
+    private ?string $description = null;
 
     /**
      * Collection of associated records.
@@ -83,9 +83,9 @@ class Set extends Entity
     /**
      * Get the description of this set.
      *
-     * @return string The set description
+     * @return ?string The set description or NULL
      */
-    public function getDescription(): string
+    public function getDescription(): ?string
     {
         return $this->description;
     }
@@ -120,6 +120,16 @@ class Set extends Entity
         return $this->records->toArray();
     }
 
+    /**
+     * Whether this set has a description.
+     *
+     * @return bool TRUE if description exists, FALSE otherwise
+     */
+    public function hasDescription(): bool
+    {
+        return isset($this->description);
+    }
+
     /**
      * Whether this set contains any records.
      *
@@ -148,19 +158,23 @@ class Set extends Entity
     /**
      * Set the description for this set.
      *
-     * @param string $description The description
+     * @param ?string $description The description
      *
      * @return void
      *
      * @throws ValidationFailedException
      */
-    public function setDescription(string $description): void
+    public function setDescription(?string $description): void
     {
-        try {
-            $this->description = $this->validateXml($description);
-        } catch (ValidationFailedException $exception) {
-            throw $exception;
+        if (isset($description)) {
+            $description = trim($description);
+            try {
+                $description = $this->validateXml($description);
+            } catch (ValidationFailedException $exception) {
+                throw $exception;
+            }
         }
+        $this->description = $description;
     }
 
     /**
@@ -180,11 +194,11 @@ class Set extends Entity
      *
      * @param string $spec The set spec
      * @param ?string $name The name of the set (defaults to spec)
-     * @param string $description The description of the set
+     * @param ?string $description The description of the set
      *
      * @throws ValidationFailedException
      */
-    public function __construct(string $spec, ?string $name = null, string $description = '')
+    public function __construct(string $spec, ?string $name = null, string $description = null)
     {
         try {
             $this->spec = $this->validateRegEx($spec, '/^([A-Za-z0-9\-_\.!~\*\'\(\)])+(:[A-Za-z0-9\-_\.!~\*\'\(\)]+)*$/');
diff --git a/src/Middleware/ListSets.php b/src/Middleware/ListSets.php
index 60a1ceb..b9fc022 100644
--- a/src/Middleware/ListSets.php
+++ b/src/Middleware/ListSets.php
@@ -90,7 +90,7 @@ class ListSets extends Middleware
             $setName = $document->createElement('setName', $oaiSet->getName());
             $set->appendChild($setName);
 
-            if ($oaiSet->getDescription() !== '') {
+            if ($oaiSet->hasDescription()) {
                 $setDescription = $document->createElement('setDescription');
                 $set->appendChild($setDescription);