Possible Clues:

• Glass half empty
• No musical info coming back
• Gloomy in local eating empty 'Scotch' dish
• Meaning of '-' on a battery terminal
• That's not positive
• Vie in tussle with agent? No
• It is found up in Geneva, shot as part of a film that doesn't illustrate the positives
• Critical as musical knowledge shown up
• Less than nothing
• It's said of people who are unenthusiastic or pessimistic