Set span context destination service name and type to empty string (#…

…1564)

This commit updates the Span context destination service name
and type to set them to empty string by default.

Both fields are marked as obsolete and will be removed in a
future version, but need to be sent as empty strings for
older APM server compatibility, which validates the presence
of these fields.

Fixes #1563

src/Elastic.Apm/Api/Destination.cs

@@ -73,8 +73,8 @@ public class DestinationService
 			/// Identifier for the destination service (e.g. 'http://elastic.co', 'elasticsearch', 'rabbitmq')"
 			/// </summary>
 			[MaxLength]
-			[Obsolete("This field will be removed in future versions")]
-			public string Name { get; set; }
+			[Obsolete("This field is unused by Elastic APM and will be removed in a future version")]
+			public string Name { get; set; } = string.Empty;
 
 			/// <summary>
 			/// Identifier for the destination service resource being operated on (e.g. 'http://elastic.co:80', 'elasticsearch',
@@ -87,8 +87,8 @@ public class DestinationService
 			/// Type of the destination service (e.g. 'db', 'elasticsearch'). Should typically be the same as span.type.
 			/// </summary>
 			[MaxLength]
-			[Obsolete("This field will be removed in future versions")]
-			public string Type { get; set; }
+			[Obsolete("This field is unused by Elastic APM and will be removed in a future version")]
+			public string Type { get; set; } = string.Empty;
 		}
 
 		/// <summary>

test/Elastic.Apm.Tests/SerializationTests.cs

@@ -463,6 +463,15 @@ public void System_Should_Serialize_ConfiguredHostName_And_DetectedHostName()
 			detectedHostName.Should().NotBeNull();
 		}
 
+		[Fact]
+		public void SpanContext_Destination_Service_Should_Serialize_Name_And_Type_As_Empty_String_By_Default()
+		{
+			var destinationService = new Destination.DestinationService();
+
+			var json = _payloadItemSerializer.Serialize(destinationService);
+			json.Should().Contain("\"name\":\"\"").And.Contain("\"type\":\"\"");
+		}
+
 		/// <summary>
 		/// A dummy type for tests.
 		/// </summary>