If (err) return callback(null)

This module worked fine a couple of days ago, but now it does not show me the mappings (but I can assign private => public ports) so I debugged a bit. Turns out that at the following line the callback does not include the error:

https://github.com/indutny/node-nat-upnp/blob/master/lib/nat-upnp/client.js#L89-L92

Shouldn't it return the error?

Anyway in my case the request body is the following:

``` js
{ '@':
{ 'xmlns:SOAP-ENV': 'http://schemas.xmlsoap.org/soap/envelope/',
'SOAP-ENV:encodingStyle': 'http://schemas.xmlsoap.org/soap/encoding/' },
'SOAP-ENV:Body':
{ 'SOAP-ENV:Fault':
{ faultcode: 'SOAP-ENV:Client',
faultstring: 'UPnPError',
detail:
{ UPnPError:
{ '@': { xmlns: 'urn:schemas-upnp-org:control-1-0' },
errorCode: '402',
errorDescription: 'Invalid NewPortMappingIndex' } } } } }
```

Any thoughts?

Start at lib/nat-upnp/client.js lines 89-92 and inspect how the callback handles the SOAP response shown in the issue. Reproduce or trace the failed port-mapping lookup, then verify that the callback preserves the reported error and that successful private-to-public mappings still work.

Written by the indexing model from the issue text.