some refactoring

Refactoring to avoid some exceptions

Author: vasile-baluta

src/main/java/com/ericsson/ei/handlers/HistoryExtractionHandler.java

@@ -20,6 +20,7 @@
 import com.ericsson.ei.rules.RulesObject;
 import com.fasterxml.jackson.databind.JsonNode;
 import com.fasterxml.jackson.databind.node.JsonNodeFactory;
+import com.fasterxml.jackson.databind.node.NullNode;
 import com.github.wnameless.json.flattener.JsonFlattener;
 
 import org.slf4j.Logger;
@@ -58,11 +59,13 @@ public class HistoryExtractionHandler {
     public String runHistoryExtraction(String aggregatedObjectId, RulesObject rules, String event,
             String pathInAggregatedObject) {
         JsonNode objectToMerge = extractContent(rules, event);
-        if (objectToMerge == null) {
+        if (objectToMerge instanceof NullNode) {
             return pathInAggregatedObject;
         }
 
         JsonNode ruleJson = getHistoryPathRule(rules, event);
+        if (ruleJson instanceof NullNode)
+            return pathInAggregatedObject;
         String ruleString = ruleJson.toString();
 
         // if we need to add append to an array then array_path will not be
@@ -155,7 +158,7 @@ private JsonNode getHistoryPathRule(RulesObject rulesObject, String event) {
         if (rule != null)
             return jmesPathInterface.runRuleOnEvent(rule, event);
 
-        return JsonNodeFactory.instance.objectNode();
+        return JsonNodeFactory.instance.nullNode();
     }
 
 }