diff --git a/src/definitions.ts b/src/definitions.ts
index fab7af4..fb1f854 100644
--- a/src/definitions.ts
+++ b/src/definitions.ts
@@ -1,6 +1,6 @@
 export interface FirebaseAnalyticsPlugin {
   initializeFirebase(options: FirebaseInitOptions): Promise<any>;
-  setUserId(options: { userId: string }): Promise<void>;
+  setUserId(options: { userId: string | null }): Promise<void>;
   setUserProperty(options: { name: string; value: string }): Promise<void>;
   getAppInstanceId(): Promise<{ instanceId: string }>;
   setScreenName(options: {
diff --git a/src/web.ts b/src/web.ts
index 724b0d7..cc21fb8 100644
--- a/src/web.ts
+++ b/src/web.ts
@@ -65,7 +65,7 @@ export class FirebaseAnalyticsWeb
    * @param options - userId: unique identifier of the user to log
    * Platform: Web/Android/iOS
    */
-  setUserId(options: { userId: string }): Promise<void> {
+  setUserId(options: { userId: string | null }): Promise<void> {
     return new Promise(async (resolve, reject) => {
       await this.ready;
 
@@ -74,12 +74,12 @@ export class FirebaseAnalyticsWeb
         return;
       }
 
-      const { userId } = options || { userId: undefined };
+      let { userId } = options || { userId: "" };
 
-      if (!userId) {
-        reject("userId property is missing");
-        return;
-      }
+      if (userId == undefined)
+        reject("userId property should be string or null");
+
+      if (userId == null) userId = "";
 
       this.analyticsRef.setUserId(userId);
       resolve();
@@ -101,7 +101,10 @@ export class FirebaseAnalyticsWeb
         return;
       }
 
-      const { name, value } = options || { name: undefined, value: undefined };
+      const { name, value } = options || {
+        name: undefined,
+        value: undefined,
+      };
 
       if (!name) {
         reject("name property is missing");
@@ -295,7 +298,6 @@ export class FirebaseAnalyticsWeb
         firebaseAnalyticsScript.src
       );
       resolve(null);
-    });
   }
 
   /**