Fix: Add guard against model NPE

CityDoctorParent/CityDoctorValidation/src/main/java/de/hft/stuttgart/citydoctor2/check/Checker.java

@@ -50,6 +50,7 @@ import java.util.stream.Collectors;
 import javax.annotation.Nullable;
 import javax.swing.text.html.Option;
 
+import de.hft.stuttgart.citydoctor2.database.UnconnectedCache;
 import de.hft.stuttgart.citydoctor2.utils.Pair;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
@@ -487,10 +488,11 @@ public class Checker {
         }
         fillParameterMapsWithDefaultParameter(enabledCheck, parameterMap);
         ArrayList<Check> checkList = new ArrayList<>();
+        CityObjectCache cache = model != null ? model.getCache() :  new UnconnectedCache();
         for (CheckId id : enabledCheck) {
             Check c = checkConfig.getCheckForId(id);
             //TODO: Change this to correct handling with streamchecker
-            c.init(parameterMap, parserConfig, model.getCache());
+            c.init(parameterMap, parserConfig, cache);
             checkList.add(c);
         }
         return checkList;