update: improve error handling by checking for null values in experiment key retrieval

Author: FarhanAnjum-opti

core-api/src/main/java/com/optimizely/ab/Optimizely.java

@@ -1451,7 +1451,10 @@ private Map<String, OptimizelyDecision> decideForKeys(@Nonnull OptimizelyUserCon
         for (int i = 0; i < flagsWithoutForcedDecision.size(); i++) {
             DecisionResponse<FeatureDecision> decision = decisionList.get(i);
             boolean error = decision.isError();
-            String experimentKey = decision.getResult().experiment.getKey();
+            String experimentKey = null;
+            if (decision.getResult() != null && decision.getResult().experiment != null) {
+                experimentKey = decision.getResult().experiment.getKey();
+            }
             String flagKey = flagsWithoutForcedDecision.get(i).getKey();
 
             if (error) {

core-api/src/test/java/com/optimizely/ab/OptimizelyTest.java

@@ -5044,7 +5044,7 @@ public void testDecideReturnsErrorDecisionWhenDecisionServiceFails() throws Exce
         assertNull(decision.getVariationKey());
         assertNull(decision.getRuleKey());
         assertEquals("feature_1", decision.getFlagKey());
-        assertTrue(decision.getReasons().contains("Decision service error occured for key \"feature_1\"."));
+        assertTrue(decision.getReasons().contains("Failed to fetch CMAB data for experiment exp-cmab."));
     }
 
 }