DataGridViewRow to DataRow - object reference not set to an instance

What I'm doing (or trying to do) is getting a row from DataGridView and convert it to DataRow, so I can put that DataRow into DataTable. So I searched for examples on the Web,
and people claimed they work just fine, but my doesn't.
This is my code:

DataGridViewRowCollection rows = myDataGridView.Rows;
 foreach (DataGridViewRow row in rows)
 {
    /*(1)*/ DataRow myRow = (row.DataBoundItem as DataRowView).Row;
    myDataTable.Rows.Add(myRow);
 }
 

but I get "Object reference not set to an instance of an object." on line (1).

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