anchor.diff:              |> List.map (fun (key,value) -> key, (String.quoted value, getAuth key))
               |> Map.ofList
           
  -        { PackageSources = if clearSources then sources
  -                           else 
  -                              Map.fold 
  -                                (fun acc k v -> Map.add k v acc)
  -                                nugetConfig.PackageSources
  -                                sources
  -                           |> Map.filter (fun k _ -> Set.contains k disabledSources |> not)
  +        { PackageSources = 
  +            match configNode.SelectSingleNode("//packageSources/clear") with
  +            | null -> Map.fold (fun acc k v -> Map.add k v acc) nugetConfig.PackageSources sources
  +            | _ -> sources
  +            |> Map.filter (fun k _ -> Set.contains k disabledSources |> not)
             PackageRestoreEnabled = 
               match configNode |> getNode "packageRestore" |> Option.bind (tryGetValue "enabled") with
               | Some value -> bool.Parse(value)
  
positive.code:             |> fail
  
      static member OverrideConfig nugetConfig (configNode : XmlNode) =
          let clearSources = configNode.SelectSingleNode("//packageSources/clear") <> null
  
          let getAuth key = 
              let getAuth' authNode =
                  let userName = authNode |> tryGetValue "Username"
  
negative.code:             | true -> ConfigAuthentication(username, password)
              | false -> PlainTextAuthentication(username, password)
          | _ -> failwith "invalid auth"
  
  /// Represents type of NuGet packages.config file
  type NugetPackagesConfigType = ProjectLevel | SolutionLevel
  
  