Add null/empty check for feature evaluation.

Author: jimmyca15

src/Microsoft.FeatureManagement/DynamicFeatureManager.cs

@@ -44,11 +44,21 @@ public async IAsyncEnumerable<string> GetDynamicFeatureNamesAsync([EnumeratorCan
 
         public ValueTask<T> GetVariantAsync<T, TContext>(string feature, TContext appContext, CancellationToken cancellationToken)
         {
+            if (string.IsNullOrEmpty(feature))
+            {
+                throw new ArgumentNullException(nameof(feature));
+            }
+
             return GetVariantAsync<T, TContext>(feature, appContext, true, cancellationToken);
         }
 
         public ValueTask<T> GetVariantAsync<T>(string feature, CancellationToken cancellationToken)
         {
+            if (string.IsNullOrEmpty(feature))
+            {
+                throw new ArgumentNullException(nameof(feature));
+            }
+
             return GetVariantAsync<T, object>(feature, null, false, cancellationToken);
         }
 

src/Microsoft.FeatureManagement/FeatureManager.cs

@@ -44,11 +44,21 @@ public FeatureManager(
 
         public Task<bool> IsEnabledAsync(string feature, CancellationToken cancellationToken)
         {
+            if (string.IsNullOrEmpty(feature))
+            {
+                throw new ArgumentNullException(nameof(feature));
+            }
+
             return IsEnabledAsync<object>(feature, null, false, cancellationToken);
         }
 
         public Task<bool> IsEnabledAsync<TContext>(string feature, TContext appContext, CancellationToken cancellationToken)
         {
+            if (string.IsNullOrEmpty(feature))
+            {
+                throw new ArgumentNullException(nameof(feature));
+            }
+
             return IsEnabledAsync(feature, appContext, true, cancellationToken);
         }
 

src/Microsoft.FeatureManagement/Targeting/TargetingEvaluator.cs

@@ -115,6 +115,11 @@ public static bool IsTargeted(
                 throw new ArgumentNullException(nameof(groups));
             }
 
+            if (string.IsNullOrEmpty(hint))
+            {
+                throw new ArgumentNullException(nameof(hint));
+            }
+
             string userId = ignoreCase ?
                 targetingContext.UserId.ToLower() :
                 targetingContext.UserId;
@@ -158,6 +163,11 @@ public static bool IsTargeted(
                 throw new ArgumentNullException(nameof(targetingContext));
             }
 
+            if (string.IsNullOrEmpty(hint))
+            {
+                throw new ArgumentNullException(nameof(hint));
+            }
+
             string userId = ignoreCase ?
                 targetingContext.UserId.ToLower() :
                 targetingContext.UserId;