未将对想引用设置到对象的实例 郁闷死了

private static SqlConnection con;
public static SqlConnection Con
{
get
{
string conString = ConfigurationManager.ConnectionStrings["HR"].ConnectionString;
if (con == null)
{
con = new SqlConnection(conString);
con.Open();
}
else if (con.State == System.Data.ConnectionState.Closed)
{
con.Open();
}
else if (con.State == System.Data.ConnectionState.Broken)
{
con.Close();
con.Open();
}
return con;
}
}


哪个地方出错了啊。好纠结