diff --git a/lib/optimizely/index.tests.js b/lib/optimizely/index.tests.js
index 20debfe31..dc9d6f6ed 100644
--- a/lib/optimizely/index.tests.js
+++ b/lib/optimizely/index.tests.js
@@ -17,7 +17,7 @@ import { assert, expect } from 'chai';
 import sinon from 'sinon';
 import { sprintf } from '../utils/fns';
 import { NOTIFICATION_TYPES } from '../notification_center/type';
-import Optimizely from './';
+import Optimizely, { INVALID_ATTRIBUTES, INVALID_IDENTIFIER } from './';
 import OptimizelyUserContext from '../optimizely_user_context';
 import { OptimizelyDecideOption } from '../shared_types';
 import AudienceEvaluator from '../core/audience_evaluator';
@@ -4379,14 +4379,16 @@ describe('lib/optimizely', function() {
         assert.deepEqual(userId, user.getUserId());
       });
 
-      it('should return null OptimizelyUserContext when input userId is null', function() {
-        var user = optlyInstance.createUserContext(null);
-        assert.deepEqual(null, user);
+      it('should throw error when input userId is null', function() {
+        assert.throws(() => {
+          optlyInstance.createUserContext(null);
+        }, Error, INVALID_IDENTIFIER);
       });
 
-      it('should return null OptimizelyUserContext when input userId is undefined', function() {
-        var user = optlyInstance.createUserContext(undefined);
-        assert.deepEqual(null, user);
+      it('should throw error when input userId is undefined', function() {
+        assert.throws(() => {
+          optlyInstance.createUserContext(undefined);
+        }, Error, INVALID_IDENTIFIER);
       });
 
       it('should create multiple instances of OptimizelyUserContext', function() {
@@ -4405,11 +4407,11 @@ describe('lib/optimizely', function() {
         assert.deepEqual(user2.getUserId(), userId2);
       });
 
-      it('should call the error handler for invalid user ID and return null', function() {
+      it('should call the error handler for invalid user ID and throw', function() {
         const { optlyInstance, errorNotifier, createdLogger } = getOptlyInstance({
           datafileObj: testData.getTestDecideProjectConfig(),
         });
-        assert.isNull(optlyInstance.createUserContext(1));
+        assert.throws(() => optlyInstance.createUserContext(1), Error, INVALID_IDENTIFIER);
         sinon.assert.calledOnce(errorNotifier.notify);
         // var errorMessage = errorHandler.handleError.lastCall.args[0].message;
         // assert.strictEqual(errorMessage, sprintf(INVALID_INPUT_FORMAT, 'OPTIMIZELY', 'user_id'));
@@ -4418,11 +4420,11 @@ describe('lib/optimizely', function() {
         // assert.strictEqual(logMessage, sprintf(INVALID_INPUT_FORMAT, 'OPTIMIZELY', 'user_id'));
       });
 
-      it('should call the error handler for invalid attributes and return null', function() {
+      it('should call the error handler for invalid attributes and throw', function() {
         const { optlyInstance, errorNotifier, createdLogger } = getOptlyInstance({
           datafileObj: testData.getTestDecideProjectConfig(),
         });
-        assert.isNull(optlyInstance.createUserContext('user1', 'invalid_attributes'));
+        assert.throws(() => optlyInstance.createUserContext('user1', 'invalid_attributes'), Error, INVALID_ATTRIBUTES);
         sinon.assert.calledOnce(errorNotifier.notify);
         // var errorMessage = errorHandler.handleError.lastCall.args[0].message;
         // assert.strictEqual(errorMessage, sprintf(INVALID_ATTRIBUTES, 'ATTRIBUTES_VALIDATOR'));
diff --git a/lib/optimizely/index.ts b/lib/optimizely/index.ts
index 0d6c937f8..c84d6a4cb 100644
--- a/lib/optimizely/index.ts
+++ b/lib/optimizely/index.ts
@@ -114,6 +114,8 @@ type DecisionReasons = (string | number)[];
 
 export const INSTANCE_CLOSED = 'Instance closed';
 export const ONREADY_TIMEOUT = 'onReady timeout expired after %s ms';
+export const INVALID_IDENTIFIER = 'Invalid identifier';
+export const INVALID_ATTRIBUTES = 'Invalid attributes';
 
 /**
  * options required to create optimizely object
@@ -1356,13 +1358,17 @@ export default class Optimizely extends BaseService implements Client {
    * @param  {string}          userId      (Optional) The user ID to be used for bucketing.
    * @param  {UserAttributes}  attributes  (Optional) user attributes.
    * @return {OptimizelyUserContext|null}  An OptimizelyUserContext associated with this OptimizelyClient or
-   *                                       null if provided inputs are invalid
+   *                                       throws if provided inputs are invalid
    */
-  createUserContext(userId?: string, attributes?: UserAttributes): OptimizelyUserContext | null {
+  createUserContext(userId?: string, attributes?: UserAttributes): OptimizelyUserContext {
     const userIdentifier = userId ?? this.vuidManager?.getVuid();
 
-    if (userIdentifier === undefined || !this.validateInputs({ user_id: userIdentifier }, attributes)) {
-      return null;
+    if (userIdentifier === undefined || !this.validateInputs({ user_id: userIdentifier })) {
+      throw new Error(INVALID_IDENTIFIER);
+    }
+
+    if (!this.validateInputs({}, attributes)) {
+      throw new Error(INVALID_ATTRIBUTES);
     }
 
     const userContext = new OptimizelyUserContext({
diff --git a/lib/shared_types.ts b/lib/shared_types.ts
index 0a1582e4a..93d5d4524 100644
--- a/lib/shared_types.ts
+++ b/lib/shared_types.ts
@@ -293,7 +293,7 @@ export interface OptimizelyVariable {
 export interface Client {
   // TODO: In the future, will add a function to allow overriding the VUID.
   getVuid(): string | undefined;
-  createUserContext(userId?: string, attributes?: UserAttributes): OptimizelyUserContext | null;
+  createUserContext(userId?: string, attributes?: UserAttributes): OptimizelyUserContext;
   notificationCenter: NotificationCenter;
   activate(experimentKey: string, userId: string, attributes?: UserAttributes): string | null;
   track(eventKey: string, userId: string, attributes?: UserAttributes, eventTags?: EventTags): void;