() Luca Ferrari <fluca1978@infinito.it>
() Thu, 18 Dec 2014 12:20:43 +0100

   Where CONNECTION is a symbol identifying the connection

I seem to recall that the original code used

 (interactive "sPROMPT?")

That arranges for the var to be assigned a string value.
Perhaps you can try:

 (interactive "SPROMPT?")

instead (NB: uppercase "S").  ‘C-h v interactive RET’ for details.

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