ValueError: arg is an empty sequence

[Andrew Gree]

GENERATE_ERROR
Traceback (most recent call last):
  File "./evsvg.py", line 192, in plotwh
    max_val, valueMid, timeMid, secondsMid, neg_val, msg, points = generate_points(value_cache[hashstr])
  File "./evsvg.py", line 102, in generate_points
    m = min([x for x in vals if x is not None])
ValueError: arg is an empty sequence

may be due to empty data? or d=,,,, ?