add context null check for built-in filters (#428)

Author: zhiyuanliang-ms

src/Microsoft.FeatureManagement/FeatureFilters/PercentageFilter.cs

@@ -4,6 +4,7 @@
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.Logging;
 using Microsoft.FeatureManagement.Utils;
+using System;
 using System.Threading.Tasks;
 
 namespace Microsoft.FeatureManagement.FeatureFilters
@@ -43,6 +44,11 @@ public object BindParameters(IConfiguration filterParameters)
         /// <returns>True if the feature is enabled, false otherwise.</returns>
         public Task<bool> EvaluateAsync(FeatureFilterEvaluationContext context)
         {
+            if (context == null)
+            {
+                throw new ArgumentNullException(nameof(context));
+            }
+
             //
             // Check if prebound settings available, otherwise bind from parameters.
             PercentageFilterSettings settings = (PercentageFilterSettings)context.Settings ?? (PercentageFilterSettings)BindParameters(context.Parameters);

src/Microsoft.FeatureManagement/FeatureFilters/TimeWindowFilter.cs

@@ -43,6 +43,11 @@ public object BindParameters(IConfiguration filterParameters)
         /// <returns>True if the feature is enabled, false otherwise.</returns>
         public Task<bool> EvaluateAsync(FeatureFilterEvaluationContext context)
         {
+            if (context == null)
+            {
+                throw new ArgumentNullException(nameof(context));
+            }
+
             //
             // Check if prebound settings available, otherwise bind from parameters.
             TimeWindowFilterSettings settings = (TimeWindowFilterSettings)context.Settings ?? (TimeWindowFilterSettings)BindParameters(context.Parameters);