Change how to decide between empty update and not called field file

src/Model/FileTag.php

@@ -291,9 +291,6 @@ class FileTag
         }
 
         $fields = ['file' => str_replace($pattern, '', $item['file'])];
-        if ($fields === '') {
-        	$fields = null;
-        }
 
         Item::update($fields, ['id' => $item_id]);
 

src/Model/Item.php

@@ -832,7 +832,7 @@ class Item extends BaseObject
 			$files = $fields['file'];
 			$fields['file'] = null;
 		} else {
-			$files = '';
+			$files = null;
 		}
 
 		$delivery_data = ['postopts' => defaults($fields, 'postopts', ''),