anchor.diff:      /// <returns></returns>
       [<CompiledName("GetError")>]
       let getError (value : Choice<'T, 'Error>) =
  +        // Preconditions
  +        checkNonNull "value" value
  +
           match value with
           | Choice1Of2 _ ->
               invalidArg "value" "Cannot get the error because the Choice`2 instance is a result value."
  
positive.code:     /// <returns></returns>
      [<CompiledName("BindOrRaise")>]
      let inline bindOrRaise (value : Choice<'T, #exn>) : 'T =
          match value with
          | Choice1Of2 result ->
              result
  
negative.code:     /// <returns></returns>
      [<CompiledName("FoldBack")>]
      let foldBack (folder : 'T -> 'State -> 'State) (value : Choice<'T, 'Error>) (state : 'State) : 'State =
          // Preconditions
          checkNonNull "value" value
  
          match value with
          | Choice1Of2 result ->
              folder result state
  