fix: Ensure proper handling of missing reason in EvaluationEventBuilder and add corresponding unit tests

Signed-off-by: André Silva <2493377+askpt@users.noreply.github.com>

Author: askpt

src/OpenFeature/Telemetry/EvaluationEventBuilder.cs

@@ -25,10 +25,10 @@ public static EvaluationEvent Build(HookContext<Value> hookContext, FlagEvaluati
             { TelemetryConstants.Provider, hookContext.ProviderMetadata.Name }
         };
 
-        attributes[TelemetryConstants.Reason] = !string.IsNullOrWhiteSpace(details.Reason) ? details.Reason?.ToLowerInvariant() : Reason.Unknown;
 
         var body = new Dictionary<string, object>();
 
+        attributes[TelemetryConstants.Reason] = !string.IsNullOrWhiteSpace(details.Reason) ? details.Reason?.ToLowerInvariant() : Reason.Unknown;
         attributes[TelemetryConstants.Variant] = details.Variant;
         attributes[TelemetryFlagMetadata.ContextId] = details.FlagMetadata?.GetString(TelemetryFlagMetadata.ContextId);
         attributes[TelemetryFlagMetadata.FlagSetId] = details.FlagMetadata?.GetString(TelemetryFlagMetadata.FlagSetId);

test/OpenFeature.Tests/Telemetry/EvaluationEventBuilderTests.cs

@@ -105,5 +105,27 @@ public void Build_ShouldHandleMissingFlagMetadata()
             Assert.Null(evaluationEvent.Attributes[TelemetryFlagMetadata.FlagSetId]);
             Assert.Null(evaluationEvent.Attributes[TelemetryFlagMetadata.Version]);
         }
+
+        [Theory]
+        [InlineData(null)]
+        [InlineData("")]
+        [InlineData(" ")]
+        public void Build_ShouldHandleMissingReason(string? reason)
+        {
+            // Arrange
+            var clientMetadata = new ClientMetadata("client", "1.0.0");
+            var providerMetadata = new Metadata("provider");
+            var hookContext = new HookContext<Value>("flagKey", new Value("value"), FlagValueType.Object, clientMetadata,
+                providerMetadata, EvaluationContext.Empty);
+            var flagMetadata = new ImmutableMetadata();
+            var details = new FlagEvaluationDetails<Value>("flagKey", new Value("value"), ErrorType.None,
+                reason: reason, variant: "", flagMetadata: flagMetadata);
+
+            // Act
+            var evaluationEvent = EvaluationEventBuilder.Build(hookContext, details);
+
+            // Assert
+            Assert.Equal(Reason.Unknown, evaluationEvent.Attributes[TelemetryConstants.Reason]);
+        }
     }
 }