Respect empty string enummember values

Fixes #983

Author: EdwardCooke

YamlDotNet.Analyzers.StaticGenerator/SerializableSyntaxReceiver.cs

@@ -210,7 +210,7 @@ private void HandleEnum(ITypeSymbol type)
                         if (enumMember != null)
                         {
                             var argument = enumMember.NamedArguments.FirstOrDefault(x => x.Key == "Value");
-                            if (!string.IsNullOrWhiteSpace(argument.Value.Value as string))
+                            if ((argument.Value.Value as string) != null)
                             {
                                 memberValue = (string)argument.Value.Value!;
                             }

YamlDotNet.Test/Analyzers/StaticGenerator/ObjectTests.cs

@@ -231,8 +231,8 @@ public void EnumSerializationUsesEnumMemberAttribute()
         public void EnumSerializationUsesEnumMemberAttributeWithEmptyValue()
         {
             var serializer = new StaticSerializerBuilder(new StaticContext()).Build();
-            var actual = serializer.Serialize(EnumMemberedEnum.EmptyValue);
-            Assert.Equal("EmptyValue", actual.TrimNewLines());
+            var actual = serializer.Serialize(new { Test = EnumMemberedEnum.EmptyValue });
+            Assert.Equal("Test: ''", actual.TrimNewLines());
         }
 
         [Fact]

YamlDotNet.Test/Serialization/SerializationTests.cs

@@ -1502,8 +1502,8 @@ public void EnumSerializationUsesEnumMemberAttribute()
         public void EnumSerializationUsesEnumMemberAttributeWithEmptyValue()
         {
             var serializer = new SerializerBuilder().Build();
-            var actual = serializer.Serialize(EnumMemberedEnum.EmptyValue);
-            Assert.Equal("EmptyValue", actual.TrimNewLines());
+            var actual = serializer.Serialize(new { Test = EnumMemberedEnum.EmptyValue });
+            Assert.Equal("Test: ''", actual.TrimNewLines());
         }
 
         [Fact]

YamlDotNet/Serialization/TypeInspectors/ReflectionTypeInspector.cs

@@ -59,7 +59,7 @@ public override string GetEnumValue(object enumValue)
             if (enumMembers.Length > 0)
             {
                 var attribute = enumMembers[0].GetCustomAttribute<EnumMemberAttribute>();
-                if (!string.IsNullOrWhiteSpace(attribute?.Value))
+                if (attribute?.Value != null)
                 {
                     result = attribute.Value;
                 }