Comment 2 for bug 690586

Seems to partially work, I'm still seeing this stack trace:

Traceback (most recent call last):
  File "/usr/lib/pymodules/python2.6/django/core/handlers/base.py", line 92, in get_response
    response = callback(request, *callback_args, **callback_kwargs)
  File "/opt/graphite/webapp/graphite/render/views.py", line 97, in renderView
    seriesList = evaluateTarget(target, timeInterval)
  File "/opt/graphite/webapp/graphite/render/evaluator.py", line 14, in evaluateTarget
    result = evaluateTokens(tokens, timeInterval)
  File "/opt/graphite/webapp/graphite/render/evaluator.py", line 30, in evaluateTokens
    return evaluateTokens(tokens.expression, timeInterval, originalTime)
  File "/opt/graphite/webapp/graphite/render/evaluator.py", line 62, in evaluateTokens
    return func(*args)
  File "/opt/graphite/webapp/graphite/render/functions.py", line 386, in stdev
    avg = safeDiv(safeSum(series[:time]), time)
  File "/opt/graphite/webapp/graphite/render/functions.py", line 386, in <lambda>
    avg = safeDiv(safeSum(series[:time]), time)
TypeError: unsupported operand type(s) for *: 'NoneType' and 'NoneType'