be much more resilient when getting current config of an attribute in a living partition

jastadd-mquat-eris/src/main/java/de/tudresden/inf/st/mquat/eris/coupling/ERISLivingPartition.java

@@ -79,7 +79,13 @@ public class ERISLivingPartition {
     }
 
     public Optional<ERISLPConfiguration> getConfigForAttribute(ERISAttribute attribute, boolean index) {
+        if (this.configurations == null) {
+            return Optional.empty();
+        }
         for (ERISLPConfiguration config : this.configurations) {
+            if (config == null || config.getAttributesAndKeys() == null || config.getAccessPath() == null || config.getAccessPath().getAddressingMode() == null) {
+                continue;
+            }
             if (config.getAttributesAndKeys().contains(attribute) && config.getAccessPath().getAddressingMode().equals("index") == index) {
                 return Optional.of(config);
             }