fix a error message bug
add tests
allow void as template argument
add test (template arguments as void vs. return)
add test
refine error message
Merge branch 'kazuho/issues/void-as-template-arg'
check the handling of Nullable.<void>
[refactor] in optimizer, use mixin for handling stash
[refactor] s/Util.isNativeClass/Util.rootIsNativeClass/g for better clarification
[refactor] introduce Expression#hasSideEffects
calculate static variables eagerly (than before)
ctors of some built-in classes do not have side effects
Merge branch 'kazuho/experiments/refactor-side-effect-detection'
fold-const the initexpr of static vars
fold-const the initexpr of static vars
static var initializer should respect inlined ctor
Merge branch 'kazuho/experiments/fold-const-static-initors'
add failing test (that was forgotten to be git-added)
do not use eval