From ebb1165b14b0d8f0a6151d8d323f231529e6f67e Mon Sep 17 00:00:00 2001
From: Pavel Krymets <pavel@krymets.com>
Date: Fri, 16 Nov 2018 13:57:43 -0800
Subject: [PATCH] Handle nullable enum default values (dotnet/extensions#531)

\n\nCommit migrated from https://github.com/dotnet/extensions/commit/33f839d585ae7664195008d8c9c5e317d5897510
---
 .../ParameterDefaultValue.cs                      | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/src/Shared/ParameterDefaultValue/ParameterDefaultValue.cs b/src/Shared/ParameterDefaultValue/ParameterDefaultValue.cs
index a71bad37b1..dc635bb789 100644
--- a/src/Shared/ParameterDefaultValue/ParameterDefaultValue.cs
+++ b/src/Shared/ParameterDefaultValue/ParameterDefaultValue.cs
@@ -8,6 +8,8 @@ namespace Microsoft.Extensions.Internal
 {
     internal class ParameterDefaultValue
     {
+        private static readonly Type _nullable = typeof(Nullable<>);
+
         public static bool TryGetDefaultValue(ParameterInfo parameter, out object defaultValue)
         {
             bool hasDefaultValue;
@@ -39,6 +41,19 @@ namespace Microsoft.Extensions.Internal
                 {
                     defaultValue = Activator.CreateInstance(parameter.ParameterType);
                 }
+
+                // Handle nullable enums
+                if (defaultValue != null &&
+                    parameter.ParameterType.IsGenericType &&
+                    parameter.ParameterType.GetGenericTypeDefinition() == _nullable
+                    )
+                {
+                    var underlyingType = Nullable.GetUnderlyingType(parameter.ParameterType);
+                    if (underlyingType != null && underlyingType.IsEnum)
+                    {
+                        defaultValue = Enum.ToObject(underlyingType, defaultValue);
+                    }
+                }
             }
 
             return hasDefaultValue;