why is it that when i dont give any user input the else statement isnt executed saying "no user input"? it just tells me circumference is equal to 0

 #!/usr/bin/perl

$radius_times = 2;
$radius_times_2 = 3.141592654;
$radius_times_2 *= $radius_times;

while (1) {
print "enter the radius\n";

$user_radius = <STDIN>;
chomp($user_radius);

if (defined($user_radius)) {

$user_radius *= $radius_times_2;

print "circumference is equal to $user_radius\n";
}


else {
    print "no user input";
}

}
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