spree/spree — pull request #5495 by wuboy0307 (2014-10-16 20:37:23+00:00)
Title: Not every payment method has to handle cancel

according to these two issues
https://github.com/spree/spree/issues/5307
https://github.com/netguru/spree_payu_integration/issues/5
I believe we have to check if cancel method is available before calling it.