anchor.diff:  /// Builds the result tree for a given query
   let rec private buildResolverTree (returnDef: OutputDef) (ctx: ResolveFieldContext) (fieldExecuteMap: FieldExecuteMap) (value: obj option) : AsyncVal<ResolverTree> =
       let name = ctx.ExecutionInfo.Identifier
  -    match ctx.ExecutionInfo.Kind with
  -    | ResolveNull ->
  -        asyncVal { return ResolverLeaf { Name = ctx.ExecutionInfo.Identifier; Value = None } }
  -    | ResolveEmpty ->
  -        asyncVal { return ResolverListNode { Name = ctx.ExecutionInfo.Identifier; Value = Some (upcast [ ]); Children = [| |] } }
  +    match ctx.ExecutionInfo.Kind, returnDef with
  +    | ResolveNull, (Scalar _ | Enum _ | Nullable _) ->
  +        asyncVal { return ResolverLeaf { Name = name; Value = None; DeferredValue = value } }
  +    | ResolveNull, (Object _ | Interface _ | Union _) ->
  +        asyncVal { return ResolverObjectNode { Name = name; Value = None; DeferredValue = value; Children = [| |] } }
  +    | ResolveEmpty, List _ ->
  +        asyncVal { return ResolverListNode { Name = name; Value = Some (upcast [ ]); DeferredValue = value; Children = [| |] } }
       | _ ->
           match returnDef with
           | Object objdef ->
  
positive.code:                 | Some v -> buildObjectFields fields objdef ctx fieldExecuteMap name v
                  | None ->
                      if ctx.ExecutionInfo.IsNullable
                      then asyncVal { return ResolverObjectNode { Name = name; Value = None; Children = [| |] } }
                      else nullResolverError name
              | kind -> failwithf "Unexpected value of ctx.ExecutionPlan.Kind: %A" kind
          | Scalar scalardef ->
              let name = ctx.ExecutionInfo.Identifier
              let (coerce: obj -> obj option) = scalardef.CoerceValue
              asyncVal {
                  return ResolverLeaf { Name = name; Value = value |> Option.bind(coerce) }
              }
          | Enum _ ->
              let name = ctx.ExecutionInfo.Identifier
              asyncVal {
                  let value' = value |> Option.bind(fun v ->  coerceStringValue v |> Option.map(fun v' -> v' :> obj))
                  return ResolverLeaf { Name = name; Value = value' }
              }
          | List (Output innerdef) ->
              let innerCtx =
  
negative.code:                 | None -> asyncVal { return ResolverError { Name = name; Message = ctx.Schema.ParseError (GraphQLException (sprintf "GraphQL Interface '%s' is not implemented by the type '%s'" idef.Name resolvedDef.Name)); PathToOrigin = [] } }
              | None ->
                  if ctx.ExecutionInfo.IsNullable
                  then asyncVal { return ResolverObjectNode { Name = name; Value = None; DeferredValue = value; Children = [| |] } }
                  else nullResolverError name
          | Union udef ->
              let possibleTypesFn = ctx.Schema.GetPossibleTypes
  