some fixes

certmgr/Core/Converters/Impl/EnumConverter.cs

@@ -8,36 +8,26 @@ public sealed class EnumConverter : ValueConverter<Enum>
     {
         Type resultType;
 
-        bool isNullable = targetType.IsGenericType && targetType.GetGenericTypeDefinition() == typeof(Nullable<>);
-        if (isNullable)
+        Type? underlying = Nullable.GetUnderlyingType(targetType);
+        if (underlying != null)
         {
-            Type[] args = targetType.GetGenericArguments();
-            if (args.Length != 1)
-            {
-                throw new ConverterException("Cannot convert nullable type '{0}' to enum", targetType.ToString(false));
-            }
-            if (args[0].IsEnum)
-            {
-                resultType = args[0];
-            }
-            else
-            {
-                throw new ConverterException("Cannot convert nullable type '{0}' as enum as it is not enum", targetType.ToString(false));
-            }
+            resultType = underlying;
         }
         else
         {
-            if (!targetType.IsEnum)
-            {
-                resultType = targetType;
-            }
-            else
-            {
-                throw new ConverterException("Cannot convert type '{0}' as enum as it is not enum", targetType.ToString(false));
-            }
+            resultType = targetType;
         }
 
-        object? result = Enum.Parse(resultType, rawValue, true);
-        return Task.FromResult((Enum?)result);
+        if (!resultType.IsEnum)
+        {
+            throw new ConverterException("Cannot convert type '{0}' as enum as it is not enum or nullable", targetType.ToString(false));
+        }
+
+        if (Enum.TryParse(resultType, rawValue, true, out object? result) && Enum.IsDefined(resultType, result))
+        {
+            return Task.FromResult((Enum?)result);
+        }
+
+        return Task.FromResult((Enum?)null);
     }
 }

certmgr/Core/Converters/Impl/EnumNullableConverter.cs

@@ -1,15 +0,0 @@
-namespace CertMgr.Core.Converters.Impl;
-
-public sealed class EnumNullableConverter : ValueConverter<Enum?>
-{
-    protected override Task<Enum?> DoConvertAsync(string rawValue, Type targetType, CancellationToken cancellationToken)
-    {
-        if (!targetType.IsEnum)
-        {
-            throw new ConverterException("Cannot convert type '{0}' as enum as it is not enum", targetType.Name);
-        }
-
-        object? result = Enum.Parse(targetType, rawValue, true);
-        return Task.FromResult((Enum?)result);
-    }
-}