What dws said.

I would phrase the conditions a little differently, myself. I read his conditions as, "If $email is identical to the empty string", while my brain says, "if $email is empty":

if ( 0 == length $email ) {
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Of course, it's all a matter of preference. I don't imagine there's much optimization differencee between string comparison to an empty string, and comparing zero to the length of an empty string.