How to leave loop if 2nd value is null without change 1st value in mysql

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MySQL

in loop replace name to value. but i want that if 2nd value is null then leave loop without replace 1st value.

What I have tried:

OPEN TESTPRO;
   LOOP_TESTPRO:loop
   fetch TESTPRO into C_PHD_TAG, C_PHD_MODE;
   if (NOT_FOUND=1 and tagval_not_found=1) then leave LOOP_TESTPRO;
   end if;
	 begin 
   
        set tagval=tagvalue(C_PHD_TAG, CPARAMETER_ID ,c_phd_mode  , v_start_shift_time ,  v_end_shift_time);
        select tagval, C_PHD_TAG;
        
        IF (tagval IS NULL ) THEN 
        SET tagval_not_found=1;
        END IF;        
        
        set replacevalue= REPLACE(upper(formula),upper(C_PHD_TAG), tagval);
         select replacevalue;
             
         set tagval = null;
	 end;
   end loop;
   close TESTPRO;