Dataset error -- object reference not set to an instance of an object

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C#3.0

C#

DataSet ds = new DataSet();
DataTable dt = new DataTable();
DataColumn dc1 = new DataColumn("parametername");
DataColumn dc2 = new DataColum("parametervalue");
dt.Columns.Add(dc1);
dt.Columns.Add(dc2);
ds.Tables.Add(dt);
DataRow dr = ds.Tables[0].NewRow();
SomeService.RemRequest Treq = new SomeService.RemRequest();
Treq.ModuleName = Some.Common.Warehouse.TransitConstant.ModuleName.somemodule;
Treq.FunctionName = "search";
Treq.UserRid = 63913;
dr[0] = "keyword";
dr[1] = txtSearch.Text;
dt.Rows.Add(dr);
DataRow dr2 = ds.Tables[0].NewRow();
dr2[0] = "class";
dr2[1] = "687";
dt.Rows.Add(dr2);

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get an error Object reference not set to an instance of an object

[edit]Code block added - OriginalGriff[/edit]