Without strict and warnings, numeric context will convert the empty string to 0, (as it will 'abc' and 'foo'). The real question is whether you're expecting or can tolerate an empty string at that point in your code. You'll need to show the code and say what you're trying to do to get advice on that.

How are you extracting those numbers from your string? You may want to set up an explicit numeric conversion if an empty string is a sane result.