message: use pythonic truthyness of lists
diff: @@ -111,14 +111,14 @@ def main():
  regressions.append((query_name, old_cost, new_cost))
  exit_code = 0
  - if len(improvements) > 0:
  + if improvements:
  print_banner("IMPROVEMENTS DETECTED")
  print_diffs(improvements)
  - if len(regressions) > 0:
  + if regressions:
  exit_code = 1
  print_banner("REGRESSIONS DETECTED")
  print_diffs(regressions)
  - if len(improvements) == 0 and len(regressions) == 0:
  + if not improvements and not regressions:
  print_banner("NO DIFFERENCES DETECTED")
  os.remove(OLD_DB_NAME)
  