Fixed issue #458

* Fixed exception in AdditionalColumnDataGenerator when passing null as log property value.
* Added regression tests.

Author: ckadluba

src/Serilog.Sinks.MSSqlServer/Sinks/MSSqlServer/Output/AdditionalColumnDataGenerator.cs

@@ -28,14 +28,14 @@ public KeyValuePair<string, object> GetAdditionalColumnNameAndValue(SqlColumn ad
                 : _columnHierarchicalPropertyValueResolver.GetPropertyValueForColumn(additionalColumn, properties);
 
             var columnName = additionalColumn.ColumnName;
-            if (property.Value == null)
+            if (!(property.Value is ScalarValue scalarValue))
             {
-                return new KeyValuePair<string, object>(columnName, DBNull.Value);
+                return new KeyValuePair<string, object>(columnName, property.Value.ToString());
             }
 
-            if (!(property.Value is ScalarValue scalarValue))
+            if (scalarValue.Value == null && additionalColumn.AllowNull)
             {
-                return new KeyValuePair<string, object>(columnName, property.Value.ToString());
+                return new KeyValuePair<string, object>(columnName, DBNull.Value);
             }
 
             var columnType = additionalColumn.AsDataColumn().DataType;

test/Serilog.Sinks.MSSqlServer.Tests/Misc/AdditionalPropertiesTests.cs

@@ -67,6 +67,58 @@ public void WritesLogEventWithColumnNamedProperties()
             VerifyIntegerColumnWritten(additionalColumnName2, property2Value);
         }
 
+        [Trait("Bugfix", "#458")]
+        [Fact]
+        public void WritesLogEventWithNullValueForNullableColumn()
+        {
+            // Arrange
+            const string additionalColumnName1 = "AdditionalColumn1";
+            const string additionalColumnName2 = "AdditionalColumn2";
+            var columnOptions = new MSSqlServer.ColumnOptions
+            {
+                AdditionalColumns = new List<SqlColumn>
+                {
+                    new SqlColumn
+                    {
+                        ColumnName = additionalColumnName1,
+                        DataType = SqlDbType.NVarChar,
+                        AllowNull = true,
+                        DataLength = 100
+                    },
+                    new SqlColumn
+                    {
+                        ColumnName = additionalColumnName2,
+                        DataType = SqlDbType.Int,
+                        AllowNull = true
+                    }
+                }
+            };
+
+            var messageTemplate = $"Hello {{{additionalColumnName1}}} from thread {{{additionalColumnName2}}}";
+            var property1Value = "PropertyValue1";
+            var expectedMessage = $"Hello \"{property1Value}\" from thread null";
+
+            // Act
+            Log.Logger = new LoggerConfiguration()
+                .WriteTo.MSSqlServer(
+                    DatabaseFixture.LogEventsConnectionString,
+                    sinkOptions: new MSSqlServerSinkOptions
+                    {
+                        TableName = DatabaseFixture.LogTableName,
+                        AutoCreateSqlTable = true
+                    },
+                    columnOptions: columnOptions,
+                    formatProvider: CultureInfo.InvariantCulture)
+                .CreateLogger();
+            Log.Information(messageTemplate, property1Value, null);
+            Log.CloseAndFlush();
+
+            // Assert
+            VerifyDatabaseColumnsWereCreated(columnOptions.AdditionalColumns);
+            VerifyLogMessageWasWritten(expectedMessage);
+            VerifyStringColumnWritten(additionalColumnName1, property1Value);
+        }
+
         [Fact]
         public void WritesLogEventWithCustomNamedProperties()
         {

test/Serilog.Sinks.MSSqlServer.Tests/Sinks/MSSqlServer/Output/AdditionalColumnDataGeneratorTests.cs

@@ -157,5 +157,28 @@ public void GetAdditionalColumnNameAndValueConvertsUniqueIdentifier()
             var expectedResult = Guid.Parse(propertyValue);
             Assert.Equal(expectedResult, result.Value);
         }
+
+        [Trait("Bugfix", "#458")]
+        [Fact]
+        public void GetAdditionalColumnNameAndValueConvertsNullValueForNullable()
+        {
+            // Arrange
+            const string columnName = "AdditionalProperty1";
+            int? propertyValue = null;
+            var additionalColumn = new SqlColumn(columnName, SqlDbType.Int, true);
+            var properties = new Dictionary<string, LogEventPropertyValue>();
+            _columnSimplePropertyValueResolver.Setup(r => r.GetPropertyValueForColumn(
+                It.IsAny<SqlColumn>(), It.IsAny<IReadOnlyDictionary<string, LogEventPropertyValue>>()))
+                .Returns(new KeyValuePair<string, LogEventPropertyValue>(columnName, new ScalarValue(propertyValue)));
+
+            // Act
+            var result = _sut.GetAdditionalColumnNameAndValue(additionalColumn, properties);
+
+            // Assert
+            _columnSimplePropertyValueResolver.Verify(r => r.GetPropertyValueForColumn(additionalColumn, properties), Times.Once);
+            Assert.Equal(columnName, result.Key);
+            Assert.IsType<DBNull>(result.Value);
+            Assert.Equal(DBNull.Value, result.Value);
+        }
     }
 }