Compose functions and empty values have problems

[freeformz]

2013-05-09T22:02:56.581822+00:00 app[web.5]: TypeError - nil can't be coerced into Float:
2013-05-09T22:02:56.581822+00:00 app[web.5]: /app/lib/umpire/librato_metrics.rb:74:in +' 2013-05-09T22:02:56.581822+00:00 app[web.5]: /app/lib/umpire/librato_metrics.rb:74:inblock (2 levels) in initialize'
2013-05-09T22:02:56.581822+00:00 app[web.5]: /app/lib/umpire/librato_metrics.rb:74:in each' 2013-05-09T22:02:56.581822+00:00 app[web.5]: /app/lib/umpire/librato_metrics.rb:74:ininject'
2013-05-09T22:02:56.581822+00:00 app[web.5]: /app/lib/umpire/librato_metrics.rb:74:in block in initialize' 2013-05-09T22:02:56.581822+00:00 app[web.5]: /app/lib/umpire/librato_metrics.rb:73:inmap'
2013-05-09T22:02:56.581822+00:00 app[web.5]: /app/lib/umpire/librato_metrics.rb:73:in initialize' 2013-05-09T22:02:56.581822+00:00 app[web.5]: /app/lib/umpire/librato_metrics.rb:41:innew'
2013-05-09T22:02:56.581822+00:00 app[web.5]: /app/lib/umpire/librato_metrics.rb:41:in compose_values_for_range' 2013-05-09T22:02:56.582131+00:00 app[web.5]: /app/lib/umpire/web.rb:54:infetch_points'