Cannot read property 'indexOf' of undefined

[uvarovann]

C:\Users\Andrey>node example.js
Search Welle COM Ports
C:\Users\Andrey\src\welle_serial.js:64
|| vendorId.indexOf('0483') >= 0 && productId.indexOf('5740') >= 0)) {
^

TypeError: Cannot read property 'indexOf' of undefined
at C:\Users\Andrey\src\welle_serial.js:64:29

C:\Users\Andrey>node example.js
Search Welle COM Ports
C:\Users\Andrey\src\welle_serial.js:64
|| vendorId.indexOf('0483') >= 0 && productId.indexOf('5740') >= 0)) {
^

TypeError: Cannot read property 'indexOf' of undefined
at C:\Users\Andrey\src\welle_serial.js:64:29