The developer guide for the .NET driver (Using Neo4j from .NET - Developer Guides) has an error, in the example code, it says:
return result.Single()[0].As();
That should read:
return result.Single()[0].As<string>();
The corresponding example in the codebase, and the documentation (https://neo4j.com/docs/driver-manual/1.7/get-started/#driver-get-started-hello-world-example) appears to be correct.