Fixes error that occurs when local storage is enabled.

lib/index.js

@@ -275,12 +275,14 @@ Segment.prototype.normalize = function(msg) {
   msg.writeKey = this.options.apiKey;
   ctx.userAgent = navigator.userAgent;
   if (!ctx.library) ctx.library = { name: 'analytics.js', version: this.analytics.VERSION };
-  var crossDomainId = this.getCachedCrossDomainId();
-  if (crossDomainId && this.isCrossDomainAnalyticsEnabled()) {
-    if (!ctx.traits) {
-      ctx.traits = { crossDomainId: crossDomainId };
-    } else if (!ctx.traits.crossDomainId) {
-      ctx.traits.crossDomainId = crossDomainId;
+  if (this.isCrossDomainAnalyticsEnabled()) {
+    var crossDomainId = this.getCachedCrossDomainId();
+    if (crossDomainId) {
+      if (!ctx.traits) {
+        ctx.traits = { crossDomainId: crossDomainId };
+      } else if (!ctx.traits.crossDomainId) {
+        ctx.traits.crossDomainId = crossDomainId;
+      }
     }
   }
   // if user provides campaign via context, do not overwrite with UTM qs param

test/index.test.js

@@ -505,6 +505,14 @@ describe('Segment.io', function() {
             analytics.stub(segment, 'enqueue');
           });
 
+          it('identify should not ultimately call getCachedCrossDomainId if crossDomainAnalytics is not enabled', function() {
+            segment.options.crossDomainIdServers = [];
+            var getCachedCrossDomainIdSpy = sinon.spy(segment, 'getCachedCrossDomainId');
+            segment.normalize({});
+            sinon.assert.notCalled(getCachedCrossDomainIdSpy);
+            segment.getCachedCrossDomainId.restore();
+          });
+
           it('should enqueue an id and traits', function() {
             analytics.identify('id', { trait: true }, { opt: true });
             var args = segment.enqueue.args[0];