Use standard Module(Class)#to_s
MODIFY
mrbgems/mruby-bin-mruby/bintest/mruby.rb
mrbgems/mruby-bin-mruby/bintest/mruby.rb
@@ -52,7 +52,7 @@ assert('garbage collecting built-in classes') do
NilClass = nil
GC.start
Array.dup
-print nil.class.name
+print nil.class.to_s
RUBY
script.flush
assert_equal "NilClass", `#{cmd('mruby')} #{script.path}`

Use standard Module(Class)#to_s