In my case I have found that some devices return strange output, it is in case no mgmt IP is available in sh cdp nei detail (CSS11501), older IOS or different platform.

DB<69> p $_[0]
DB<70> x $_[0]
0  "\c@\c@\c@\c@"
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My dirty hack for that was just check for valid hex-like input

          #if (substr($hex_ip,0,1) eq ""){
          if ($hex_ip !~ m/0x.*/){
          $ip = "0.0.0.0";
            }
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