Add null to customUserClaims (#958)

Author: MathBunny

src/auth/auth.ts

@@ -424,7 +424,7 @@ export class BaseAuth<T extends AbstractAuthRequestHandler> {
    * @return {Promise<void>} A promise that resolves when the operation completes
    *     successfully.
    */
-  public setCustomUserClaims(uid: string, customUserClaims: object): Promise<void> {
+  public setCustomUserClaims(uid: string, customUserClaims: object | null): Promise<void> {
     return this.authRequestHandler.setCustomUserClaims(uid, customUserClaims)
       .then(() => {
         // Return nothing on success.