.net - Cannot define T in C#

Any clue how to define T in this code?

 public static T ToEnum(this string value, T defaultValue)
        {
            if (string.IsNullOrEmpty(value))

            {
                return defaultValue;
            }

            T result;
            return Enum.TryParse(value, true, out result) ? result : defaultValue;
        }

Severity Code Description Project File Line Error CS0453 The type 'T'
must be a non-nullable value type in order to use it as parameter
'TEnum' in the generic type or method 'Enum.TryParse(string,
bool, out TEnum)'

Answer

Try using a constraint to have a value type which is a struct, for sample:

public static T ToEnum(this string value, T defaultValue)
      where T : struct 

{
    if (string.IsNullOrEmpty(value))
    {
        return defaultValue;
    }

    T result;
    return Enum.TryParse(value, true, out result) ? result : defaultValue;
}

I haven't tested it.