[iOS] JSON value '<null>' of type NSNull cannot be converted to NSString

[dylancom]

• I have updated Purchases SDK to the latest version
• I have read the Contribution Guidelines
• I have searched the Community
• I have read docs.revenuecat.com
• I have searched for existing Github issues

Describe the bug
After Purchases.configure({ apiKey: REVENUECAT_API_KEY }); is called, Xcode console logs: JSON value '<null>' of type NSNull cannot be converted to NSString. Upon refreshing the simulator the error logs again. If I remove configure, the log is gone.

Update: I found that this error is triggered when appUserID is absent.

react-native-purchases/src/purchases.ts

Line 615 in 85bba1e

appUserID,

Not explicitly setting it to null (when absent) fixes it for me, so leaving it undefined.

react-native-purchases/src/purchases.ts

Line 525 in 85bba1e

appUserID = null,

Now found that it was mentioned here that this warning can't be removed: #1196
What is the downside of passing it as undefined to native instead of null? Which removes the warning...

1. Environment
   1. Platform: iOS
   2. SDK version:
   3. OS version: 26.5
   4. Xcode/Android Studio version: 26.6
   5. React Native version: 0.87.1
   6. SDK installation (CocoaPods + version or manual): 10.9.0
   7. Error on all iOS devices