NullReferenceException when ClientKey is wrong

[gioalhaz]

If ClientKey is wrong then code below throws exception

var context = new Context()
{
    Enabled = true,
    ClientKey = SDKConnectionClientKey,
    Attributes = attrs,
    LoggerFactory = loggerFactory
};

 
 var featureFlags = new GrowthBook.GrowthBook(context);
 
 var task = featureFlags.LoadFeatures();
 task.Wait();
 
 featureFlags.IsOn("AdvancedMode");

Error log below:

dbug: GrowthBook.Api.FeatureRefreshWorker[0]
      Features GrowthBook API endpoint: 'https://cdn.growthbook.io/api/features/sdk-****'
dbug: GrowthBook.Api.FeatureRefreshWorker[0]
      Features GrowthBook API endpoint (Server Sent Events): 'https://cdn.growthbook.io/api/features/sdk-****'
info: GrowthBook.GrowthBook[0]
      Loading features from the repository
info: GrowthBook.Api.FeatureRepository[0]
      Getting features from repository, verifying cache expiration and option to force refresh
info: GrowthBook.Api.FeatureRepository[0]
      Cache has expired or option to force refresh was set, refreshing the cache from the API
dbug: GrowthBook.Api.FeatureRepository[0]
      Cache expired: 'True' and option to force refresh: '(null)'
info: GrowthBook.Api.FeatureRefreshWorker[0]
      Making an HTTP request to the default Features API endpoint 'https://cdn.growthbook.io/api/features/sdk-****'
info: GrowthBook.Api.FeatureRepository[0]
      Either cache currently has no features or the option to wait for completion was set, waiting for cache to refresh
dbug: GrowthBook.Api.FeatureRepository[0]
      Feature count: '0' and option to wait for completion: '(null)'
fail: GrowthBook.Api.FeatureRefreshWorker[0]
      HTTP request to default Features API endpoint 'https://cdn.growthbook.io/api/features/sdk-****' resulted in a BadRequest status code
info: GrowthBook.GrowthBook[0]
      Loading features has completed, retrieved '' features
fail: GrowthBook.GrowthBook[0]
      Encountered an unhandled exception while executing 'EvalFeature'
      System.NullReferenceException: Object reference not set to an instance of an object.
         at GrowthBook.GrowthBook.EvalFeature(String featureId)

Other then that, there is no way to determine was LoadFeatures successful or not. No result code, no error code, nothing :(

[vazarkevych]

Hi @mjr444 . We have reproduced the bug when LoadFeatures() failed due to an invalid ClientKey, the SDK would set Features to null, causing NullReferenceException crashes when developers tried to use feature flags afterward. There was also no clear error feedback about what went wrong.

What Was Fixed:

• Prevented Crashes - Features property is never set to null, so IsOn() and GetFeatureValue() always work
• Better Error Messages - HTTP errors now include specific messages like "This usually indicates an invalid ClientKey"
• New Result Method - Added LoadFeaturesWithResult() that returns success/failure details without throwing exceptions
• Custom Exceptions - Created meaningful exception types with HTTP status codes for better debugging
• Graceful Degradation - Apps continue working with default feature values even when loading fails

Result:
The SDK now handles invalid ClientKey scenarios gracefully, provides clear error feedback to developers, and never crashes the application. Backward compatibility is maintained while adding modern error handling patterns.

Here you check our #53 for that.