At the moment, we can write ```nu $env.foo = $env.bar = "baz" ``` and even ```nu let $foo = let $bar = "baz" ``` without any warning, but the resulting values are ```nu $env.foo == null $env.bar == "baz" ``` which is most likely not what was expected. I think this should be reported as a warning (or even an error if there are no actual use cases for this syntax).