getVariationForFeatureInRollout to return null decisionResponse when rolloutRulesLength is zero (#423)

Author: mnoman09

core-api/src/main/java/com/optimizely/ab/bucketing/DecisionService.java

@@ -283,6 +283,9 @@ DecisionResponse<FeatureDecision> getVariationForFeatureInRollout(@Nonnull Featu
 
         // for all rules before the everyone else rule
         int rolloutRulesLength = rollout.getExperiments().size();
+        if (rolloutRulesLength == 0) {
+            return new DecisionResponse(new FeatureDecision(null, null, null), reasons);
+        }
         String bucketingId = getBucketingId(userId, filteredAttributes);
 
         Variation variation;