Generalized nullables exist in Base already (<a href="http:&#x2F;&#x2F;docs.julialang.org&#x2F;en&#x2F;release-0.4&#x2F;manual&#x2F;types&#x2F;#nullable-types-representing-missing-values" rel="nofollow">http:&#x2F;&#x2F;docs.julialang.org&#x2F;en&#x2F;release-0.4&#x2F;manual&#x2F;types&#x2F;#nulla...</a>), unless you had something else in mind.