not defined is fine, but not is very low precedence. That is,

if (not defined($pname) && $pname ne ''){
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is parsed the same as

if (not (defined($pname) && $pname ne '')){
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instead of

if ((not defined($pname)) && $pname ne ''){
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Also, if $pname isn't defined, then it can't possibly equal '', so you probably need to change your conditions a bit (probably you mean something like

if (!defined($pname) || $pname eq ''){
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but it's possible you want something else.)