Why a template with Nullable does not compile?

[Victor Porton]

On Tuesday, 12 March 2019 at 15:26:05 UTC, Victor Porton wrote:
> template FieldInfo(T, Nullable!T default_) {
> }
>
> On Tuesday, 12 March 2019 at 09:05:36 UTC, Nicholas Wilson 
> wrote:
>> It seems to be getting confused between the two types of 
>> Nullable, namely:
>> Nullable(T), and
>> Nullable(T, T defaultVal)
>
> I don't understand why exactly it is getting confused. How can 
> it decide that "Nullable!T default_" is a two-arguments 
> template when it is so not "Nullable!(T, default_)"? Please 
> explain the EXACT cause of the error.

My question why it is getting confused was not answered.