Problema select count(*)

USE tempdb;
GO


CREATE PROCEDURE dbo.proc_Conta
  @Righe int = NULL OUTPUT
AS
BEGIN

  SET NOCOUNT ON;

  CREATE TABLE #tempTable
  (
      ID int IDENTITY PRIMARY KEY CLUSTERED
    , Nome varchar(30) NOT NULL
  )

  INSERT INTO #tempTable (Nome)
  VALUES ('Alessandro Alpi')
  INSERT INTO #tempTable (Nome)
  VALUES ('Lorenzo Benaglia')
  INSERT INTO #tempTable (Nome)
  VALUES ('David De Giacomi')
  INSERT INTO #tempTable (Nome)
  VALUES ('Marco Caruso')
  INSERT INTO #tempTable (Nome)
  VALUES ('Matteo Raumer')

  SELECT 
      ID
    , Nome
  FROM
    #tempTable

  SET @Righe = @@ROWCOUNT

END
GO

DECLARE @Righe int
SET @Righe = NULL

EXEC dbo.proc_Conta @Righe OUTPUT

SELECT Cotenggio = @Righe

DROP PROCEDURE dbo.proc_Conta
GO