GitLab

Use Qlambda as interrim value of Vminibuffer_completing_file_name.
(Fcompleting_read, do_completion, Fminibuffer_complete_word):
If Vminibuffer_completing_file_name equals Qlambda, treat it as Qnil.
(syms_of_minibuf) <minibuffer-completing-file-name>: Document lambda.