uvm Error-[IND] Identifier not declared

Hello ,

My code for sequence is follows , 

`ifndef seq_stimulus
`define seq_stimulus

import uvm_pkg::*;
`include "uvm_macros.svh"

class seq_stimulus extends stimulus;

`uvm_object_utils(seq_stimulus)

stimulus req;
function new(string name = "seq_stimulus");
super.new(name);
endfunction

virtual task body();
req = stimulus::type_id::create("req");
`uvm_do(req);
`uvm_info(get_type_name(),$sformatf("data = 'h%0h,valid= 'h%0h",req.data,req.valid),UVM_HIGH)

endtask

endclass

`endif

but it gives error:

Error-[IND] Identifier not declared
/classes_v/seq_stimulus.sv, 20
Identifier 'create_item' has not been declared yet. If this error is not
expected, please check if you have set `default_nettype to none.

Error-[IND] Identifier not declared
seq_stimulus.sv, 20
Identifier 'start_item' has not been declared yet. If this error is not
expected, please check if you have set `default_nettype to none.

Error-[IND] Identifier not declared
seq_stimulus.sv, 20
Identifier 'finish_item' has not been declared yet. If this error is not
expected, please check if you have set `default_nettype to none.

please suggest thnks