What is a "Missing file from filelist 'install-info'" warning for?

Why when I install some packages using apt, I receive a message like this:

dpkg: aviso: falta ficheiro de lista de ficheiros 'install-info'; assumindo que o pacote não tem actualmente ficheiros instalados

Translating to

dpkg: Warning: Missing file from filelist 'install-info'; assuming that package has not installed files

It's not critical, because I can install something, but... Why this message?