Why does System.ArgumentNullException appear when I add values ​​from the DataGridView to the listbox?

Question

C++ / C#

Error: System.ArgumentNullException: "Value cannot be null.
Parameter name: item"

for (int i = 0; i < filmsDataGridView.RowCount; i++)
            {          
                listBox1.Items.Add(filmsDataGridView.Rows[i].Cells[7].Value);
            }

Answer 1

Your error is due to the fact that filmsDataGridView.Rows[i].Cells[7].Value in some cases you have = null, and null cannot be inserted into CombopBox
Always convert nulls to an empty string like
or like this:
listBox1.Items.Add(filmsDataGridView.Rows[i].Cells[7].Value?.ToString() ?? String.Empty);