While `return` and `return nil` are for most intents and purposes
identical, there are situations where they're not. For example,
calculating the amount of values via the `select()` function will yield
varying results:
```lua
local function nothing() return end
local function null() return nil end
select('#', nothing()) -- 0
select('#', null()) -- 1
```
`vim.tbl_get` currently returns both nil and no results, which makes it
unreliable to use in certain situations without manually accounting for
these discrepancies.