Version Used:
Microsoft Visual Studio Community 2017
Version 15.2 (26430.16) Release
VisualStudio.15.Release/15.2.0+26430.16
Microsoft .NET Framework
Version 4.6.01586

Steps to Reproduce:
This produces "Use of unassigned local variable" but it should not.

if ((variable is Type x) == false) {
    return;
}
x.Function();

This should be logically equivalent to code above and it works fine.

if (!(variable is Type x)) {
    return;
}
x.Function();

We like to use == flase instead of ! in our code base for added readability. Unfortunately this does not work with above statement :/ Would it be possible to add it?

Thanks!