prevent errors to be written multiple times in qualityADE

CityDoctorParent/CityDoctorModel/src/main/java/de/hft/stuttgart/citydoctor2/utils/QualityADEUtils.java

@@ -19,7 +19,9 @@
 package de.hft.stuttgart.citydoctor2.utils;
 
 import java.util.ArrayList;
+import java.util.HashSet;
 import java.util.List;
+import java.util.Set;
 
 import org.citygml4j.model.citygml.ade.ADEComponent;
 import org.citygml4j.model.citygml.core.CityModel;
@@ -65,7 +67,8 @@ public class QualityADEUtils {
 				res.setResult(ResultType.OK);
 			} else {
 				res.setResult(ResultType.ERROR);
-				for (CheckError e : errors) {
+				Set<CheckError> errorSet = new HashSet<>(errors);
+				for (CheckError e : errorSet) {
 					e.convertToQualityAdeDatastructure().ifPresent(res.getErrors()::add);
 				}
 			}