fix: preserve_line_style assume the type of the operation data

lib/src/models/rules/insert.dart

@@ -568,6 +568,7 @@ class PreserveInlineStylesRule extends InsertRule {
       if (prevData.endsWith('\n')) {
         /// If current line is empty get attributes from a prior line
         final currLine = itr.next();
+        if (currLine.data is String) {
           final currData = currLine.data as String?;
           if (currData != null && (currData.isEmpty || currData[0] == '\n')) {
             if (prevData.trimRight().isEmpty) {
@@ -582,6 +583,7 @@ class PreserveInlineStylesRule extends InsertRule {
           }
         }
       }
+    }
 
     final attributes = <String, dynamic>{};
     if (prev.attributes != null) {