From 58f79cef11f4d4d11f6cd190e8032be2ef15653b Mon Sep 17 00:00:00 2001
From: Sipke Schoorstra <sipkeschoorstra@outlook.com>
Date: Tue, 23 Mar 2021 21:02:19 +0100
Subject: [PATCH] Add support for nullable enum properties

---
 .../Activities/CallRingGroup.cs               |  7 ++++++
 .../ActivityPropertyOptionsResolver.cs        | 24 +++++++++++++++++--
 .../ActivityPropertyUIHintResolver.cs         |  3 ++-
 3 files changed, 31 insertions(+), 3 deletions(-)

diff --git a/src/activities/Elsa.Activities.Telnyx/Activities/CallRingGroup.cs b/src/activities/Elsa.Activities.Telnyx/Activities/CallRingGroup.cs
index 565d1db60..a10197331 100644
--- a/src/activities/Elsa.Activities.Telnyx/Activities/CallRingGroup.cs
+++ b/src/activities/Elsa.Activities.Telnyx/Activities/CallRingGroup.cs
@@ -34,6 +34,13 @@ namespace Elsa.Activities.Telnyx.Activities
             get => GetState<RingGroupStrategy>();
             set => SetState(value);
         }
+        
+        [ActivityProperty]
+        public RingGroupStrategy? StrategyTest
+        {
+            get => GetState<RingGroupStrategy?>();
+            set => SetState(value);
+        }
 
         [ActivityProperty(Hint =
             "The 'from' number to be used as the caller id presented to the destination ('To' number). The number should be in +E164 format. This attribute will default to the 'From' number of the original call if omitted.")]
diff --git a/src/core/Elsa.Core/Metadata/ActivityPropertyOptionsResolver.cs b/src/core/Elsa.Core/Metadata/ActivityPropertyOptionsResolver.cs
index 52d96f114..95c03887b 100644
--- a/src/core/Elsa.Core/Metadata/ActivityPropertyOptionsResolver.cs
+++ b/src/core/Elsa.Core/Metadata/ActivityPropertyOptionsResolver.cs
@@ -1,6 +1,8 @@
 using System;
+using System.Collections.Generic;
 using System.Linq;
 using System.Reflection;
+using AutoMapper.Internal;
 using Elsa.Attributes;
 using Elsa.Design;
 using Humanizer;
@@ -26,8 +28,8 @@ namespace Elsa.Metadata
 
             if (activityPropertyAttribute.OptionsProvider == null)
             {
-                if (activityPropertyInfo.PropertyType.IsEnum)
-                    return activityPropertyInfo.PropertyType.GetEnumNames().Select(x => new SelectListItem(x.Humanize(LetterCasing.Title), x));
+                if (TryGetEnumOptions(activityPropertyInfo, out var items))
+                    return items;
 
                 return activityPropertyAttribute.Options;
             }
@@ -38,5 +40,23 @@ namespace Elsa.Metadata
             var provider = (IActivityPropertyOptionsProvider) ActivatorUtilities.GetServiceOrCreateInstance(scope.ServiceProvider, providerType);
             return provider.GetOptions(activityPropertyInfo);
         }
+
+        private bool TryGetEnumOptions(PropertyInfo activityPropertyInfo, out IList<SelectListItem>? items)
+        {
+            var isNullable = activityPropertyInfo.PropertyType.IsNullableType();
+            var propertyType = isNullable ? activityPropertyInfo.PropertyType.GetTypeOfNullable() : activityPropertyInfo.PropertyType;
+
+            items = null;
+
+            if (!propertyType.IsEnum)
+                return false;
+            
+            items = propertyType.GetEnumNames().Select(x => new SelectListItem(x.Humanize(LetterCasing.Title), x)).ToList();
+
+            if (isNullable)
+                items.Insert(0, new SelectListItem("-", ""));
+
+            return true;
+        }
     }
 }
\ No newline at end of file
diff --git a/src/core/Elsa.Core/Metadata/ActivityPropertyUIHintResolver.cs b/src/core/Elsa.Core/Metadata/ActivityPropertyUIHintResolver.cs
index 7f407fd59..67b018bb8 100644
--- a/src/core/Elsa.Core/Metadata/ActivityPropertyUIHintResolver.cs
+++ b/src/core/Elsa.Core/Metadata/ActivityPropertyUIHintResolver.cs
@@ -1,5 +1,6 @@
 using System.Collections;
 using System.Reflection;
+using AutoMapper.Internal;
 using Elsa.Attributes;
 using Elsa.Design;
 
@@ -25,7 +26,7 @@ namespace Elsa.Metadata
             if (typeof(IEnumerable).IsAssignableFrom(type))
                 return ActivityPropertyUIHints.Dropdown;
             
-            if (type.IsEnum)
+            if (type.IsEnum || type.IsNullableType() && type.GetTypeOfNullable().IsEnum)
                 return ActivityPropertyUIHints.Dropdown;
 
             return ActivityPropertyUIHints.SingleLine;