This is a harmless warning you can safely ignore. It is caused by a (harmless) bug on the module that I have just fixed in version 1.76_02.

In any case, die_on_error is not on Net::SFTP API. If you are using Net::SFTP::Foreign::Compat you should stick to that. Though, If you are writing your module from scratch, just use the much friendly Net::SFTP::Foreign module.