anchor.diff:  
   type ITypeHandler =
       abstract member GetKnownTypes : CoreVariableType seq
  -    abstract member GetMapping : targetType : System.Type -> TypeMapping option
  +    abstract member GetMapping : targetType : Type -> TypeMapping option
   
   type ZeroTypeHandler() =
       interface ITypeHandler with
  
positive.code: type CollectionTypeContext(rootHandler : ITypeHandler) =
      let translateCollection
          (emptyCons : ConstructorInfo)
          (icollection : System.Type)
          (clrElementType : System.Type)
          value =
          let add = icollection.GetMethod("Add", [|clrElementType|])
          match value with
  
negative.code:     static member Default = defaultInstance :> ITypeHandler
      interface ITypeHandler with
          member this.GetKnownTypes = context.GetKnownTypes
          member this.GetMapping(targetType) =
              let mutable cached = None
              if (not <| mappingCache.TryGetValue(targetType, &cached)) then
                  cached <- context.GetMapping(targetType)
                  mappingCache.[targetType] <- cached
              cached