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Value of %s can be "0"; test with defined()

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Value of %s can be "0"; test with defined()
(W) In a conditional expression, you used < HANDLE>, <*> (glob), each(), or readdir() as a boolean value. Each of these constructs can return a value of ``0''; that would make the conditional expression false, which is probably not what you intended. When using these constructs in conditional expressions, test their values with the defined operator.

Source: what's new for perl5.004
Copyright: Larry Wall, et al.
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