pub(crate) fn expect_module(self, msg: &str) -> Result<Module, RubyError> {
        if self.is_module() {
            Ok(Module::new(self))
        } else {
            Err(VMError::wrong_type(msg, "Module", self))
        }
    }
Returns `&ClassInfo` if `self` is a Module.
When `self` is not a Module, returns `TypeError`.
ruruby/src/value/value.rs