Fix nullability for enums (#1382)

Author: leotsarev

src/JoinRpg.Helpers/DisplayAttributeHelper.cs

@@ -30,7 +30,7 @@ public static string GetDisplayName([NotNull] this MemberInfo propertyInfo)
         /// <summary>
         /// Returns name specified by <see cref="DisplayNameAttribute"/> or <see cref="DisplayAttribute"/>
         /// </summary>
-        public static string GetDisplayName([NotNull] this Enum enumValue)
+        public static string GetDisplayName<TEnum>([NotNull] this TEnum enumValue) where TEnum : notnull, Enum
         {
             if (enumValue is null)
             {

src/JoinRpg.Portal/Views/Shared/DisplayTemplates/ClaimFullStatusView.cshtml

@@ -4,6 +4,6 @@
     @Html.DisplayFor(model => model.ClaimStatus)
     @if (Model.ClaimDenialStatus != null && Model.AccessArguments.MasterAccess)
     {
-        <text >(@Model.ClaimDenialStatus.GetDisplayName())</text>
+        <text >(@Model.ClaimDenialStatus?.GetDisplayName())</text>
     }
 </text>

src/JoinRpg.Portal/Views/ShowSchedule/_AppointmentPartial.cshtml

@@ -32,7 +32,7 @@
      slots="@slots"
      all-rooms="@(Model.AllRooms.ToString())"
      error-mode="@((Model.ErrorType == AppointmentErrorType.Intersection).ToString())"
-     errors="@(Model.ErrorType.HasValue ? Model.ErrorType.GetDisplayName() : "")">
+     errors="@(Model.ErrorType.HasValue ? Model.ErrorType?.GetDisplayName() : "")">
     <div class="appointment-interior" title="@title">
         <div class="appointment-header"><a href="@url" target="@target">@Model.DisplayName</a></div>
         @if (Model.ErrorType == AppointmentErrorType.NotLocated)

src/JoinRpg.WebPortal.Models/Exporters/CustomExporter.cs

@@ -91,7 +91,14 @@ private static ITableColumn BoolColumn(Expression<Func<TRow, bool>> func, string
         }
 
         [MustUseReturnValue]
-        protected ITableColumn EnumColumn(Expression<Func<TRow, Enum>> func)
+        protected ITableColumn EnumColumn<TEnum>(Expression<Func<TRow, Nullable<TEnum>>> func) where TEnum : struct, Enum
+        {
+            var member = func.AsPropertyAccess();
+            return new TableColumn<string>(member, r => func.Compile()(r)?.GetDisplayName());
+        }
+
+        [MustUseReturnValue]
+        protected ITableColumn EnumColumn<TEnum>(Expression<Func<TRow, TEnum>> func) where TEnum : struct, Enum
         {
             var member = func.AsPropertyAccess();
             return new TableColumn<string>(member, r => func.Compile()(r).GetDisplayName());