Used for custom serialization and deserialization of enum type fields, tolerating parse errors

TolerantStringEnumConverter.cs

public class TolerantStringEnumConverter<TEnum> : JsonConverter<TEnum>
{
    const string DefaultIndex = "0";
    const string DefaultEnumNone = "None";

    public override TEnum Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
        bool isNullable = IsNullableType(typeToConvert);
        Type enumType = GetEnumType(typeToConvert);

        if (enumType.BaseType != typeof(Enum))
            throw new InvalidCastException("TEnum is not an enumeration type");

        string[] names = Enum.GetNames(enumType);

        if (reader.TokenType == JsonTokenType.String)
        {
            string enumText = reader.GetString();

            if (!string.IsNullOrWhiteSpace(enumText))
            {
                string match = names
                    .FirstOrDefault(n => string.Equals(n, enumText, StringComparison.OrdinalIgnoreCase));

                if (match != null)
                    return (TEnum)Enum.Parse(enumType, match);
            }
        }
        else if (TryGetAsIntValue(reader, out int enumVal))
        {
           int[] values = (int[])Enum.GetValues(enumType);

           if (values.Contains(enumVal))
                return (TEnum)Enum.Parse(enumType, enumVal.ToString());
        }

        if (!isNullable)
        {
            string defaultName = names
                .FirstOrDefault(n => string.Equals(n, DefaultEnumNone, StringComparison.OrdinalIgnoreCase));

            if (defaultName != null)
                return (TEnum)Enum.Parse(enumType, defaultName);
        }

        return (TEnum)Enum.Parse(enumType, DefaultIndex);
    }

    public override void Write(Utf8JsonWriter writer, TEnum value, JsonSerializerOptions options)
        => writer.WriteStringValue(value.ToString());

    private bool IsNullableType(Type type)
        => (type.IsGenericType && type.GetGenericTypeDefinition() == typeof(Nullable<>));

    private Type GetEnumType(Type type)
        => IsNullableType(type) ? Nullable.GetUnderlyingType(type) : type;

    private bool TryGetAsIntValue(Utf8JsonReader reader, out int value)
    {
        value = 0;

        if (reader.TokenType != JsonTokenType.Number)
            return false;

        return (reader.TryGetInt32(out value));
    }
}