Adds support of other Nullable types binding

lib/ApiMultipartFormDataFormatter/Services/Implementations/BaseMultiPartFormdataModelBinderService.cs

@@ -26,27 +26,37 @@ public object BuildModel(PropertyInfo propertyInfo, object value)
             var underlyingType = Nullable.GetUnderlyingType(propertyType);
 
             // Property is GUID.
-            if ((propertyType == typeof(Guid) || underlyingType == typeof(Guid)) && Guid.TryParse(value.ToString(), out var guid))
+            if (propertyType == typeof(Guid) && Guid.TryParse(value.ToString(), out var guid))
                 return guid;
+            if (underlyingType == typeof(Guid))
+            {
+                if (Guid.TryParse(value.ToString(), out guid))
+                    return guid;
+                return null;
+            }
 
             // Property is Enum.
             if (propertyType.IsEnum)
                 return convertToEnum(propertyType, value.ToString());
             if (underlyingType != null && underlyingType.IsEnum)
+            {
+                if (string.IsNullOrWhiteSpace(value.ToString()))
+                    return null;
                 return convertToEnum(underlyingType, value.ToString());
+            }
+
+            // Other Nullable types
+            if (underlyingType != null)
+            {
+                if (string.IsNullOrEmpty(value.ToString())) return null;
+                propertyType = underlyingType;
+            }
 
             return Convert.ChangeType(value, propertyType);
         }
 
         object convertToEnum(Type type, string val)
         {
-//            if (type.GetEnumNames().Contains(val, StringComparer.InvariantCultureIgnoreCase))
-//                return Enum.Parse(type, val, true);
-//
-//            if (!int.TryParse(val, out var num)) return null;
-
-//            return Enum.ToObject(type, num);
-
             if (int.TryParse(val, out var num))
                 return Enum.ToObject(type, num);