fix the case when relation is set to null

Reviewed-on: #20

src/PersistentData/PersistentDataManager.php

@@ -115,7 +115,7 @@ class PersistentDataManager implements IPersistentDataManager
 
             if (count($modified) > 0) {
                 if ($model instanceof ModelWithSlug && isset($modified['slug'])) {
-                    $modified['slug'] = $this->generateUniqueSlug($model, $modified['slug']);
+                    $diff['slug']['new'] = $modified['slug'] = $this->generateUniqueSlug($model, $modified['slug']);
                 }
 
                 $modify->setId($id);

src/View/Linker.php

@@ -97,8 +97,13 @@ class Linker
 
         fwrite($outputFileHandle, $extra[0]);
         while (($line = fgets($inputFileHandle)) !== false) {
+            if (preg_match('/^\s*@include\((.*)\)\s*$/', $line, $matches) === 1) {
+                $include = file_get_contents(ROOT . '/views/' . $matches[1] . '.php');
+                fwrite($outputFileHandle, $include);
+            } else {
                 fwrite($outputFileHandle, $line);
             }
+        }
         fwrite($outputFileHandle, $extra[1]);
 
         fclose($inputFileHandle);