For a null date, I usually just use Date() (Dates.Date()), which returns 
Jan 1, 0001.  Also, you know that there is already a method to check 
whether or not a year is a leap year right? 

Dates.isleapyear(y), returns a Bool. 
 http://docs.julialang.org/en/release-0.4/manual/dates/

On Monday, February 8, 2016 at 10:08:25 PM UTC-5, Michael Landis wrote:
>
> I'm so confused....
>
> I thought this would be cool:
> isLeapYr(yr::Int64) = yr % 400 == 0  ||  (yr % 4 == 0  &&  yr % 100 != 0)
> LeapDay(yr) = isLeapYr(yr) ? Date(yr,2,29) : Nullable{Date}()
>
> lp15 = LeapDay(2015) --> Nullable{Date}()
> lp16 = LeapDay(2016) --> 2016-02-29
>
> no surprises there, but when I test the return values ...
>
> isnull( lp15 ) --> true
> isnull( lp16 ) -->  MethodError: `isnull` has no method matching isnull( 
> ::Date )
>
> What IS the secret Nullable{Date} formulation?
>

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