WebAdaptor Object reference not set to an instance of an object.

<?xml version="1.0" encoding="utf-8"?>
<Config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<GISServer>
<Nodes />
<SiteUrl />
<HttpPort>6080</HttpPort>
<HttpsPort>6443</HttpsPort>
<Id />
<SharedKey />
<Protocol>HTTP</Protocol>
</GISServer>
<Portal>
<URL>http://your domain:7080</URL>
<HttpPort>7080</HttpPort>
<HttpsPort>7443</HttpsPort>
<Id>guid</Id>
<SharedKey>YourKey</SharedKey>
</Portal>
<Version>10.2.1</Version>
</Config>