diff --git a/GrowthBook/Api/FeatureRefreshWorker.cs b/GrowthBook/Api/FeatureRefreshWorker.cs
index 56f2cbd..c8253a5 100644
--- a/GrowthBook/Api/FeatureRefreshWorker.cs
+++ b/GrowthBook/Api/FeatureRefreshWorker.cs
@@ -188,7 +188,7 @@ private IDictionary<string, Feature> GetFeaturesFrom(string json)
         {
             var featuresResponse = JsonConvert.DeserializeObject<FeaturesResponse>(json);
 
-            if (featuresResponse.EncryptedFeatures.IsMissing())
+            if (featuresResponse.EncryptedFeatures.IsNullOrWhitespace())
             {
                 _logger.LogInformation($"API response JSON contained no encrypted features, returning '{featuresResponse.FeatureCount}' unencrypted features");
                 return featuresResponse.Features;
diff --git a/GrowthBook/Extensions/ValidationExtensions.cs b/GrowthBook/Extensions/ValidationExtensions.cs
index e0b01ce..bedb81f 100644
--- a/GrowthBook/Extensions/ValidationExtensions.cs
+++ b/GrowthBook/Extensions/ValidationExtensions.cs
@@ -15,6 +15,6 @@ internal static class ValidationExtensions
         /// </remarks>
         /// <param name="value">The string to verify.</param>
         /// <returns>True if null, empty, or whitespace, false otherwise.</returns>
-        public static bool IsMissing(this string value) => string.IsNullOrWhiteSpace(value);
+        public static bool IsNullOrWhitespace(this string value) => string.IsNullOrWhiteSpace(value);
     }
 }
diff --git a/GrowthBook/FeatureResult.cs b/GrowthBook/FeatureResult.cs
index 88eb75a..8fd5536 100644
--- a/GrowthBook/FeatureResult.cs
+++ b/GrowthBook/FeatureResult.cs
@@ -12,7 +12,7 @@ public class FeatureResult
         /// <summary>
         /// Represents possible values for the source of a feature result.
         /// </summary>
-        public static class SourceIs
+        public static class SourceId
         {
             public const string UnknownFeature = "unknownFeature";
             public const string DefaultValue = "defaultValue";
diff --git a/GrowthBook/GrowthBook.cs b/GrowthBook/GrowthBook.cs
index ded7463..885aab0 100644
--- a/GrowthBook/GrowthBook.cs
+++ b/GrowthBook/GrowthBook.cs
@@ -190,7 +190,7 @@ public FeatureResult EvalFeature(string featureId)
             {
                 if (!Features.TryGetValue(featureId, out Feature feature))
                 {
-                    return GetFeatureResult(null, FeatureResult.SourceIs.UnknownFeature);
+                    return GetFeatureResult(null, FeatureResult.SourceId.UnknownFeature);
                 }
 
                 foreach (FeatureRule rule in feature?.Rules ?? Enumerable.Empty<FeatureRule>())
@@ -227,7 +227,7 @@ public FeatureResult EvalFeature(string featureId)
                             }
                         }
 
-                        return GetFeatureResult(rule.Force, FeatureResult.SourceIs.Force);
+                        return GetFeatureResult(rule.Force, FeatureResult.SourceId.Force);
                     }
 
                     var experiment = new Experiment
@@ -253,10 +253,10 @@ public FeatureResult EvalFeature(string featureId)
                         continue;
                     }
 
-                    return GetFeatureResult(result.Value, FeatureResult.SourceIs.Experiment, experiment, result);
+                    return GetFeatureResult(result.Value, FeatureResult.SourceId.Experiment, experiment, result);
                 }
 
-                return GetFeatureResult(feature.DefaultValue ?? null, FeatureResult.SourceIs.DefaultValue);
+                return GetFeatureResult(feature.DefaultValue ?? null, FeatureResult.SourceId.DefaultValue);
             }
             catch(Exception ex)
             {
@@ -264,10 +264,10 @@ public FeatureResult EvalFeature(string featureId)
 
                 if (!Features.TryGetValue(featureId, out Feature feature))
                 {
-                    return GetFeatureResult(null, FeatureResult.SourceIs.UnknownFeature);
+                    return GetFeatureResult(null, FeatureResult.SourceId.UnknownFeature);
                 }
 
-                return GetFeatureResult(feature.DefaultValue ?? null, FeatureResult.SourceIs.DefaultValue);
+                return GetFeatureResult(feature.DefaultValue ?? null, FeatureResult.SourceId.DefaultValue);
             }
         }
 
@@ -343,7 +343,7 @@ private ExperimentResult RunExperiment(Experiment experiment, string featureId)
 
             // 3. Use the override value from the query string if one is specified.
 
-            if (!Url.IsMissing())
+            if (!Url.IsNullOrWhitespace())
             {
                 var overrideValue = ExperimentUtilities.GetQueryStringOverride(experiment.Key, Url, experiment.Variations.Count);
 
@@ -374,7 +374,7 @@ private ExperimentResult RunExperiment(Experiment experiment, string featureId)
 
             var hashValue = Attributes.GetHashAttributeValue(experiment.HashAttribute);
 
-            if (hashValue.IsMissing())
+            if (hashValue.IsNullOrWhitespace())
             {
                 _logger.LogDebug($"Aborting experiment, unable to locate a value for the experiment hash attribute '{experiment.HashAttribute}'");
                 return GetExperimentResult(experiment, featureId: featureId);
@@ -462,7 +462,7 @@ private bool IsFilteredOut(IEnumerable<Filter> filters)
             {
                 var hashValue = Attributes.GetHashAttributeValue(filter.Attribute);
 
-                if (hashValue.IsMissing())
+                if (hashValue.IsNullOrWhitespace())
                 {
                     _logger.LogDebug($"Attributes are missing a filter's hash attribute of '{filter.Attribute}', marking as filtered out");
                     return true;
diff --git a/GrowthBook/Utilities/ExperimentUtilities.cs b/GrowthBook/Utilities/ExperimentUtilities.cs
index 7da35d5..f1ca3c7 100644
--- a/GrowthBook/Utilities/ExperimentUtilities.cs
+++ b/GrowthBook/Utilities/ExperimentUtilities.cs
@@ -19,14 +19,14 @@ internal static class ExperimentUtilities
         /// <returns>The overridden variation id, or null if not found.</returns>
         public static int? GetQueryStringOverride(string id, string url, int numVariations)
         {
-            if (url.IsMissing())
+            if (url.IsNullOrWhitespace())
             {
                 return null;
             }
 
             var res = new Uri(url);
 
-            if (res.Query.IsMissing())
+            if (res.Query.IsNullOrWhitespace())
             {
                 return null;
             }
@@ -34,7 +34,7 @@ internal static class ExperimentUtilities
             NameValueCollection qs = HttpUtility.ParseQueryString(res.Query);
             var variation = qs.Get(id);
 
-            if (variation.IsMissing())
+            if (variation.IsNullOrWhitespace())
             {
                 return null;
             }