Fix max method on empty array in chargeback storage report

[lpichler]

Issue is that when we have result as empty array(It is because we don't have any VimPerformance yet) of method VimPerformanceStates#sub_metric_rollups then on this empty array can be called method max and then we have nil in value:

[].max => nil

Note: for sum it is ok:

[].sum => 0

Error message

➜  manageiq git:(master) ✗ ./tools/generate_report.rb 'storage-volume'
** override_gem: manageiq-ui-classic, [{:path=>"/Users/liborpichler/manageiq/manageiq-ui-classic"}], caller: /Users/liborpichler/manageiq/manageiq/bundler.d/Gemfile.dev.rb
** Using session_store: ActionDispatch::Session::MemCacheStore
Generating report... storage-volume
/Users/liborpichler/manageiq/manageiq/app/models/chargeback_rate_detail.rb:104:in `block in find_rate': undefined method `*' for nil:NilClass (NoMethodError)
	from /Users/liborpichler/manageiq/manageiq/.bundle/ruby/2.4.0/gems/activerecord-5.0.6/lib/active_record/relation/delegation.rb:38:in `each'
	from /Users/liborpichler/manageiq/manageiq/.bundle/ruby/2.4.0/gems/activerecord-5.0.6/lib/active_record/relation/delegation.rb:38:in `each'
	from /Users/liborpichler/manageiq/manageiq/app/models/chargeback_rate_detail.rb:104:in `detect'
	from /Users/liborpichler/manageiq/manageiq/app/models/chargeback_rate_detail.rb:104:in `find_rate'
	from /Users/liborpichler/manageiq/manageiq/app/models/chargeback_rate_detail.rb:123:in `hourly_cost'
	from /Users/liborpichler/manageiq/manageiq/app/models/chargeback_rate_detail.rb:228:in `metric_and_cost_by'
	from /Users/liborpichler/manageiq/manageiq/app/models/chargeback_rate_detail.rb:90:in `charge'
	from /Users/liborpichler/manageiq/manageiq/app/models/chargeback.rb:137:in `block (2 levels) in calculate_costs'
	from /Users/liborpichler/manageiq/manageiq/app/models/chargeback.rb:136:in `each'
	from /Users/liborpichler/manageiq/manageiq/app/models/chargeback.rb:136:in `block in calculate_costs'
	from /Users/liborpichler/manageiq/manageiq/app/models/chargeback.rb:135:in `each'
	from /Users/liborpichler/manageiq/manageiq/app/models/chargeback.rb:135:in `calculate_costs'
	from /Users/liborpichler/manageiq/manageiq/app/models/chargeback.rb:33:in `block in build_results_for_report_chargeback'
	from /Users/liborpichler/manageiq/manageiq/app/models/chargeback/consumption_history.rb:27:in `block (2 levels) in for_report'
	from /Users/liborpichler/manageiq/manageiq/app/models/chargeback/consumption_history.rb:25:in `each'
	from /Users/liborpichler/manageiq/manageiq/app/models/chargeback/consumption_history.rb:25:in `block in for_report'
	from /Users/liborpichler/manageiq/manageiq/app/models/chargeback/consumption_history.rb:9:in `each'
	from /Users/liborpichler/manageiq/manageiq/app/models/chargeback/consumption_history.rb:9:in `each_cons'
	from /Users/liborpichler/manageiq/manageiq/app/models/chargeback/consumption_history.rb:9:in `for_report'
	from /Users/liborpichler/manageiq/manageiq/app/models/chargeback.rb:20:in `build_results_for_report_chargeback'
	from /Users/liborpichler/manageiq/manageiq/app/models/chargeback_vm.rb:62:in `build_results_for_report_ChargebackVm'
	from /Users/liborpichler/manageiq/manageiq/app/models/miq_report/generator.rb:199:in `_generate_table'
	from /Users/liborpichler/manageiq/manageiq/app/models/miq_report/generator.rb:173:in `block in generate_table'
	from /Users/liborpichler/manageiq/manageiq/app/models/user.rb:246:in `with_user'

Links

• https://bugzilla.redhat.com/show_bug.cgi?id=1517956

@miq-bot assign @gtanzillo

@miq-bot add_label bug, chargeback, blocker

[miq-bot]

Checked commits lpichler/manageiq@6757fe6~...71d629e with ruby 2.3.3, rubocop 0.47.1, haml-lint 0.20.0, and yamllint 1.10.0
2 files checked, 0 offenses detected
Everything looks fine. 🏆

[lpichler]

@miq-bot add_label gaprindashvili/yes

[lpichler]

@simaishi

[simaishi]

Gaprindashvili backport details:

$ git log -1
commit 1ad25ed36517a2e917365b2b4374ab338d25b77a
Author: Gregg Tanzillo <gtanzill@redhat.com>
Date:   Fri Dec 1 10:37:25 2017 -0500

    Merge pull request #16575 from lpichler/fix_empty_array_in_chargeback_storage_report
    
    Fix max method on empty array in chargeback storage report
    (cherry picked from commit a06bd40f283a83c4d58cf6edf312993158f23e18)
    
    https://bugzilla.redhat.com/show_bug.cgi?id=1517956