Error: add-to-list cannot use lexical var ...

[Jambunathan K]

I happened to make some modifications to vc-dir.el recently and tried
using `add-to-list' as part of these modifications.

Add the below snippet somewhere in vc-dir.el and byte-compile it.
    (let (l)
      (add-to-list 'l "testing"))

You will see an error like.
    vc-dir.el:54:1:Warning: Unused lexical variable `l'
    vc-dir.el:54:7:Error: add-to-list cannot use lexical var `l'

I should say the results are not along the expected lines.  Can someone
explain it to me?
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