if(undef($nomSQL)) { $nomSQL = "";} is probably not what you want. You are undefining $nomSQL, rather than testing for definedness. You probably want this:

if( not defined $nomSQL ) {
    $nomSQL = '';
}
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...also written as:

unless( defined $nomSQL ) {
    $nomSQL = '';
}
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...but the latter reads less clearly to me.