[r=dave-cheney],[bug=1251076] Workaround LP 1251076
[r=dave-cheney],[bug=1251076] Workaround LP 1251076

gccgo appears to get confused and thinks that out[1] is not nil when in fact it is an interface value of type error and value nil.

This workaround solves the problem by leaving error as nil if in fact it was nil and causes no harm for gc because the predicates above assert that if out[1] is not nil, then it is an error type.

https://codereview.appspot.com/83340045/
reedobrien/store