diff --git a/Kitodo/src/main/java/org/kitodo/production/helper/Helper.java b/Kitodo/src/main/java/org/kitodo/production/helper/Helper.java
index 04c2770c743..955cd7c66f3 100644
--- a/Kitodo/src/main/java/org/kitodo/production/helper/Helper.java
+++ b/Kitodo/src/main/java/org/kitodo/production/helper/Helper.java
@@ -490,6 +490,7 @@ private static String appendUnusedInsertions(String message, String... insertion
         StringBuilder messageBuilder = new StringBuilder(message);
         for (String insertion : insertions) {
             String separator = ": ";
+            insertion = Objects.toString(insertion);
             if (!messageBuilder.toString().contains(insertion)) {
                 messageBuilder.append(separator).append(insertion);
             }