Treating empty string in form post as null for nullable value types

src/Components/Endpoints/src/FormMapping/Converters/NullableConverter.cs

@@ -14,6 +14,15 @@ public bool CanConvertSingleValue() => _nonNullableConverter is ISingleValueConv
 
     public bool TryConvertValue(ref FormDataReader reader, string value, out T? result)
     {
+        if (string.IsNullOrEmpty(value))
+        {
+            // Form post sends empty string for a form field that does not have a value,
+            // in case of nullable value types, that should be treated as null and
+            // should not be parsed for its underlying type
+            result = null;
+            return true;
+        }
+
         var converter = (ISingleValueConverter<T>)_nonNullableConverter;
 
         if (converter.TryConvertValue(ref reader, value, out var converted))
@@ -30,17 +39,20 @@ public bool TryConvertValue(ref FormDataReader reader, string value, out T? resu
 
     [RequiresDynamicCode(FormMappingHelpers.RequiresDynamicCodeMessage)]
     [RequiresUnreferencedCode(FormMappingHelpers.RequiresUnreferencedCodeMessage)]
-    internal override bool TryRead(ref FormDataReader context, Type type, FormDataMapperOptions options, out T? result, out bool found)
+    internal override bool TryRead(ref FormDataReader reader, Type type, FormDataMapperOptions options, out T? result, out bool found)
     {
-        if (!(_nonNullableConverter.TryRead(ref context, type, options, out var innerResult, out found) && found))
+        // Donot call non-nullable converter's TryRead method, it will fail to parse empty
+        // string. Call the TryConvertValue method above (similar to ParsableConverter) so
+        // that it can handle the empty string correctly
+        found = reader.TryGetValue(out var value);
+        if (!found)
         {
-            result = null;
-            return false;
+            result = default;
+            return true;
         }
         else
         {
-            result = innerResult;
-            return true;
+            return TryConvertValue(ref reader, value!, out result!);
         }
     }
 }