fix: keep documents with a null required attribute updatable

A document stored before an attribute became required holds null for it,
and updates validate the merged document, so every update of that
document failed with "Missing required attribute". When the current
document already holds null, the attribute may stay null on update.
Creating a document without it, or clearing a stored value, still fails.

Author: HarshMN2345

src/Database/Validator/Structure.php

@@ -267,6 +267,11 @@ protected function checkForAllRequiredValues(array $structure, array $attributes
             $keys[$name] = $attribute; // List of allowed attributes to help find unknown ones
 
             if ($required && !isset($structure[$name])) {
+                // Documents stored before the attribute became required hold null, and may keep it
+                if ($this->currentDocument !== null && $this->currentDocument->getAttribute($name) === null) {
+                    continue;
+                }
+
                 $this->message = 'Missing required attribute "'.$name.'"';
                 return false;
             }
@@ -333,6 +338,10 @@ protected function checkForInvalidAttributeValues(Document $document, array $str
                 continue;
             }
 
+            if (is_null($value) && $this->currentDocument !== null && $this->currentDocument->getAttribute($key) === null) {
+                continue;
+            }
+
             if ($type === Database::VAR_RELATIONSHIP) {
                 continue;
             }

tests/unit/Validator/StructureTest.php

@@ -242,6 +242,38 @@ public function testRequiredKeys(): void
         $this->assertEquals('Invalid document structure: Missing required attribute "title"', $validator->getDescription());
     }
 
+    public function testRequiredKeyStoredAsNull(): void
+    {
+        $document = [
+            '$collection' => ID::custom('posts'),
+            'description' => 'Demo description',
+            'rating' => 5,
+            'price' => 1.99,
+            'published' => true,
+            'feedback' => 'team@appwrite.io',
+            '$createdAt' => '2000-04-01T12:00:00.000+00:00',
+            '$updatedAt' => '2000-04-01T12:00:00.000+00:00'
+        ];
+
+        $validator = new Structure(
+            new Document($this->collection),
+            Database::VAR_INTEGER,
+            currentDocument: new Document(['title' => null])
+        );
+
+        $this->assertTrue($validator->isValid(new Document($document)), $validator->getDescription());
+        $this->assertTrue($validator->isValid(new Document([...$document, 'title' => null])), $validator->getDescription());
+
+        $validator = new Structure(
+            new Document($this->collection),
+            Database::VAR_INTEGER,
+            currentDocument: new Document(['title' => 'My Title'])
+        );
+
+        $this->assertFalse($validator->isValid(new Document([...$document, 'title' => null])));
+        $this->assertEquals('Invalid document structure: Missing required attribute "title"', $validator->getDescription());
+    }
+
     public function testNullValues(): void
     {
         $validator = new Structure(