don't let user fall outside of last bucket in rollout

evaluate_flag.js

@@ -295,7 +295,7 @@ function variationForUser(r, user, flag) {
   if (r.variation != null) {
     // This represets a fixed variation; return it
     return r.variation;
-  } else if (r.rollout != null) {
+  } else if (r.rollout != null && r.rollout.variations != null && r.rollout.variations.length > 0) {
     // This represents a percentage rollout. Assume
     // we're rolling out by key
     const bucketBy = r.rollout.bucketBy != null ? r.rollout.bucketBy : 'key';
@@ -308,6 +308,13 @@ function variationForUser(r, user, flag) {
         return variate.variation;
       }
     }
+
+    // The user's bucket value was greater than or equal to the end of the last bucket. This could happen due
+    // to a rounding error, or due to the fact that we are scaling to 100000 rather than 99999, or the flag
+    // data could contain buckets that don't actually add up to 100000. Rather than returning an error in
+    // this case (or changing the scaling, which would potentially change the results for *all* users), we
+    // will simply put the user in the last bucket.
+    return r.rollout.variations[r.rollout.variations.length - 1].variation;
   }
 
   return null;