in reply to Why does an undef argument in a join produce this warning?

The second argument is not undef. The double quotes 
"$ENV{'HTTP_HOSTS'} "

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says that you are trying to concatanate an undef value with, in this case, a space. That is what Perl is complaining about. Remove the quotes and the result is 
HTML

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nit: You don't need the quotes around the hash key either.

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Re^2: Why does an undef argument in a join produce this warning?
by Anonymous Monk on Apr 24, 2008 at 06:23 UTC
    Thanks. you and chromatic were right
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      You already have the solution for this case. If you ever have issues with unwanted warnings again, you should know that there can be specifically deactivated locally in the current scope.

      E.g. if you know that one function can cause this warning and the only way around would be massive use of if defined you can just say no warnings 'uninitialized'; to tell Perl that you don't want this specific warning inside the current scope, i.e. sub function or { } block, etc.

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        Of course, in this case, the warning pointed to a bug...
        --
        Wade
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