diff --git a/src/ConfigCatClient/Evaluation/RolloutEvaluator.cs b/src/ConfigCatClient/Evaluation/RolloutEvaluator.cs
index 09ca9bba..c6d5a21a 100644
--- a/src/ConfigCatClient/Evaluation/RolloutEvaluator.cs
+++ b/src/ConfigCatClient/Evaluation/RolloutEvaluator.cs
@@ -244,8 +244,11 @@ private bool TryEvaluatePercentageOptions(PercentageOption[] percentageOptions,
                 continue;
             }
 
-            var percentageOptionValue = percentageOption.Value.GetValue(throwIfInvalid: false);
-            logBuilder?.NewLine().Append($"- Hash value {hashValue} selects % option {i + 1} ({percentageOption.Percentage}%), '{percentageOptionValue ?? EvaluateLogHelper.InvalidValuePlaceholder}'.");
+            if (logBuilder is not null)
+            {
+                var percentageOptionValue = percentageOption.Value.GetValue(throwIfInvalid: false) ?? EvaluateLogHelper.InvalidValuePlaceholder;
+                logBuilder.NewLine().Append($"- Hash value {hashValue} selects % option {i + 1} ({percentageOption.Percentage}%), '{percentageOptionValue}'.");
+            }
 
             result = new EvaluateResult(percentageOption, matchedTargetingRule: targetingRule, matchedPercentageOption: percentageOption);
             return true;