OZG-3260 return unmodifiable Map after remove processed data

semantik-adapter/src/main/java/de/itvsh/kop/eingangsadapter/semantik/enginebased/AbstractFileMapper.java

@@ -23,6 +23,7 @@
  */
 package de.itvsh.kop.eingangsadapter.semantik.enginebased;
 
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -82,9 +83,9 @@ public abstract class AbstractFileMapper implements EngineBasedMapper {
 	}
 
 	protected FormData removeProcessedData(FormData formData) {
-		Map<String, Object> mutableMap = new HashMap<>(formData.getFormData());
-		mutableMap.remove(MAPPED_FILES);
-		return formData.toBuilder().formData(Map.copyOf(mutableMap)).build();
-	}
+		var cleanedFormData = new HashMap<String, Object>(formData.getFormData());
+		cleanedFormData.remove(MAPPED_FILES);
 
-}
+		return formData.toBuilder().formData(Collections.unmodifiableMap(cleanedFormData)).build();
+	}
+}
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