Generic string to enum extension method with default value

I'm still at my early beginning in C# and I'm trying to implement Enum/converter converters.

All my enums has a NotDefined value equals to -1.

I would like to implement a generic extension method to get an enum from a string base on the the enum description (which mostly differ in spaces and cases).

public static T ToEnum<T>(this string value) where T : struct 
{
    foreach (T e in Enum.GetValues(typeof(T)))
    {
        if (e.GetDescription() ==value)
        {
            return e;
        }
    }
    
    // Doesn't work..
    // How can I return T.NotDefined? - I don't really want to throw something here
    return (T)-1; 
}

PS I initially found the GetDescription() implementation thanks to this thread : Enum ToString with user friendly strings which helps me a lot :-) .

Does anyone have an insight about my issue?

Many thanks!