The quick dirty ugly way would be to define your own error handler, and ignore it.

I did that here, adding in

sub my_error()
{
}
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And defining an error tag above your GLOBAL line, like

ERROR => \&my_error,
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When I run, I get no error about global_password not existing.
Of course, YMMV. Personally, I wouldn't ignore any errors if I could help it.

Or, you could use the CREATE tag to make variables automatically that don't exist and set them to their default values.