Change variation_key to '' instead of null in metadata

Author: yavorona

packages/optimizely-sdk/lib/core/event_builder/index.js

@@ -103,6 +103,12 @@ function getImpressionEventParams(configObj, experimentId, variationId, ruleKey,
   if (experimentId !== null) {
     campaignId = projectConfig.getLayerId(configObj, experimentId);
   }
+
+  let variationKey = projectConfig.getVariationKeyFromId(configObj, variationId);
+  if (variationKey === null) {
+    variationKey = '';
+  }
+
   var impressionEventParams = {
     decisions: [
       {
@@ -113,7 +119,7 @@ function getImpressionEventParams(configObj, experimentId, variationId, ruleKey,
           flag_key: flagKey,
           rule_key: ruleKey,
           rule_type: ruleType,
-          variation_key: projectConfig.getVariationKeyFromId(configObj, variationId),
+          variation_key: variationKey,
         }
       },
     ],

packages/optimizely-sdk/lib/core/project_config/index.js

@@ -279,7 +279,7 @@ export var getExperimentAudienceConditions = function(projectConfig, experimentK
  * Get variation key given experiment key and variation ID
  * @param  {Object} projectConfig Object representing project configuration
  * @param  {string} variationId   ID of the variation
- * @return {string} Variation key or null if the variation ID is not found
+ * @return {string|null} Variation key or null if the variation ID is not found
  */
 export var getVariationKeyFromId = function(projectConfig, variationId) {
   if (projectConfig.variationIdMap.hasOwnProperty(variationId)) {