diff --git a/Fengling.RiskControl.Domain/Aggregates/RiskRules/RiskRule.cs b/Fengling.RiskControl.Domain/Aggregates/RiskRules/RiskRule.cs
index 7394e7f..c2f1330 100644
--- a/Fengling.RiskControl.Domain/Aggregates/RiskRules/RiskRule.cs
+++ b/Fengling.RiskControl.Domain/Aggregates/RiskRules/RiskRule.cs
@@ -53,8 +53,8 @@ public class RiskRule : Entity<long>, IAggregateRoot
         UpdatedAt = DateTime.UtcNow;
     }
 
-    public T GetConfig<T>() where T : class
+    public T? GetConfig<T>() where T : class
     {
-        return System.Text.Json.JsonSerializer.Deserialize<T>(ConfigJson)!;
+        return System.Text.Json.JsonSerializer.Deserialize<T>(ConfigJson);
     }
 }
diff --git a/Fengling.RiskControl.Domain/Aggregates/RiskScores/RiskScore.cs b/Fengling.RiskControl.Domain/Aggregates/RiskScores/RiskScore.cs
index 2fcba61..7266882 100644
--- a/Fengling.RiskControl.Domain/Aggregates/RiskScores/RiskScore.cs
+++ b/Fengling.RiskControl.Domain/Aggregates/RiskScores/RiskScore.cs
@@ -43,11 +43,14 @@ public class RiskScore : Entity<long>, IAggregateRoot
         RiskLevel = RiskLevel.Low;
     }
 
+    private static readonly int HIGH_THRESHOLD = 70;
+    private static readonly int MEDIUM_THRESHOLD = 30;
+
     private void RecalculateScore()
     {
         TotalScore = _factors.Sum(f => f.Points);
-        RiskLevel = TotalScore >= 70 ? RiskLevel.High :
-                   TotalScore >= 30 ? RiskLevel.Medium :
+        RiskLevel = TotalScore >= HIGH_THRESHOLD ? RiskLevel.High :
+                   TotalScore >= MEDIUM_THRESHOLD ? RiskLevel.Medium :
                    RiskLevel.Low;
     }