# Void not defined (version problem?)

**URL:** <https://discourse.julialang.org/t/void-not-defined-version-problem/14183>\
**Category:** General Usage\
**Created:** [August 28, 2018, 11:49am UTC](https://discourse.julialang.org/t/void-not-defined-version-problem/14183 "2018-08-28T11:49:03Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![Jeroen\_Mebis](https://avatars.discourse-cdn.com/v4/letter/j/e99b99/32.png) [@Jeroen\_Mebis](https://discourse.julialang.org/u/Jeroen_Mebis)\
**Post date:** [August 28, 2018, 11:49am UTC](https://discourse.julialang.org/t/void-not-defined-version-problem/14183/1 "2018-08-28T11:49:03Z")

</div>

Hi  
A friend has written some code in a previous Julia version. I want to run it in version 1.0 but I’m getting some errors like this one:

```julia
if jbdy["installationDate"] isa Void
      date_instal = NaN
end

```

but I get this error:

> UndefVarError: Void not defined  
> in top-level scope at base\none  
> in …

What is the fault?

---

<div class="post-metadata">

**Author:** ![stevengj](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/stevengj/32/71_2.png) [@stevengj](https://discourse.julialang.org/u/stevengj)\
**Post date:** [August 28, 2018, 11:53am UTC](https://discourse.julialang.org/t/void-not-defined-version-problem/14183/2 "2018-08-28T11:53:27Z")

</div>

> [@Jeroen\_Mebis](#):
>
> A friend has written some code in a previous Julia version. I want to run it in version 1.0 but I’m getting some errors like this one:

Don’t use 1.0, use 0.7. Julia 0.7 is basically the same thing as 1.0 but with deprecation warnings for old features, so that most old code will continue to run (warnings instead of errors). It is especially important to use 0.7 when upgrading old code.

In the case of `Void`, in Julia 0.7 you will get a deprecation message indicating that it is now called `Nothing`:

```julia
julia> Void
WARNING: Base.Void is deprecated, use Nothing instead.
 in module Main
Nothing

```

That being said, rather than checking `x isa Nothing`, the fastest and most idiomatic code is normally `x === nothing` (yes, `===`, not `==`, for efficiency).

---

<div class="post-metadata">

**Author:** ![Jeroen\_Mebis](https://avatars.discourse-cdn.com/v4/letter/j/e99b99/32.png) [@Jeroen\_Mebis](https://discourse.julialang.org/u/Jeroen_Mebis)\
**Post date:** [August 28, 2018, 12:30pm UTC](https://discourse.julialang.org/t/void-not-defined-version-problem/14183/3 "2018-08-28T12:30:17Z")

</div>

Ok, thank you for the quick respons!