Allow null value

src/Sanitizer.php

@@ -58,8 +58,13 @@ public static function create(array $config): SanitizerInterface
         return SanitizerBuilder::createDefault()->build($config);
     }
 
-    public function sanitize(string $html): string
+    public function sanitize(?string $html = null): ?string
     {
+        if(!$html)
+        {
+            return null;
+        }
+
         $sanitized = $this->doSanitize($html);
 
         if ($this->logger) {

src/SanitizerInterface.php

@@ -20,5 +20,5 @@
  */
 interface SanitizerInterface
 {
-    public function sanitize(string $html): string;
+    public function sanitize(?string $html = null): ?string;
 }

tests/SimpleSanitizerTest.php

@@ -24,6 +24,14 @@ public function createSanitizer(): SanitizerInterface
     public function provideFixtures(): array
     {
         return array_merge(parent::provideFixtures(), [
+            /*
+             * Null value
+             */
+            [
+                null,
+                null
+            ]
+
             /*
              * Normal tags
              */