Description of problem:
unable to generate chargeback based on metering for vms with traceback in logs :
[----] E, [2018-06-26T14:52:00.406817 #18623:d39118] ERROR -- : [NoMethodError]: undefined method `sum' for #<Chargeback::ConsumptionWithoutRollups:0x000000001aa82068>  Method:[block in method_missing]
[----] E, [2018-06-26T14:52:00.407002 #18623:d39118] ERROR -- : /var/www/miq/vmdb/app/models/chargeable_field.rb:45:in `measure_metering'
/var/www/miq/vmdb/app/models/metering.rb:45:in `block in calculate_costs'
/opt/rh/rh-ruby23/root/usr/share/ruby/set.rb:306:in `each_key'
/opt/rh/rh-ruby23/root/usr/share/ruby/set.rb:306:in `each'
/var/www/miq/vmdb/app/models/metering.rb:19:in `calculate_costs'

Version-Release number of selected component (if applicable):
5.9.2.4

How reproducible:
customer environment

Steps to Reproduce:
1.create a report based on metering for vms
2.queue a run
3.

Actual results:
run ends up failing with an error.

Expected results:
run ends successfully

Additional info:
customer logs attached privately