Error converting DBNull object datagridview

I have the following code:

This is declared the variable at the beginning of all my code:

int editado = 0;

This method I use in a button.

public void Insertar
                   { try
        {
            for (int i = 0; i < dgvFormulacion.Rows.Count - 1; i++)
            {
                Program.con.Close();
                Program.con.Open();

                cm = new SqlCommand("insert into Formulacion values(@NombreConcepto,@cantidad,@precio,@editado", Program.con);
                cm.Parameters.AddWithValue("@NombreConcepto", dgvFormulacion.Rows[i].Cells["MateriaPrima"].Value);

                if (dgvFormulacion.Rows[i].Cells["PrecioUnitario"].Value == null)
                {
                    dgvFormulacion.Rows[i].Cells["PrecioUnitario"].Value = "0";
                }
                if (dgvFormulacion.Rows[i].Cells["Cant"].Value == null)
                {
                    dgvFormulacion.Rows[i].Cells["Cant"].Value = "0";
                }

                if (Convert.ToBoolean(dgvFormulacion.Rows[i].Cells["Editar"].Value) == true)//////Linea de error DBnull
                {
                    editado = 1;
                }
                else if (Convert.ToBoolean(dgvFormulacion.Rows[i].Cells["Editar"].Value) == false)
                {
                    editado = 0;
                }                   
                cm.Parameters.AddWithValue("@editado", editado);

                cm.Parameters.AddWithValue("@precio", dgvFormulacion.Rows[i].Cells["PrecioUnitario"].Value);
                cm.Parameters.AddWithValue("@cantidad", dgvFormulacion.Rows[i].Cells["Cant"].Value);

                cm.ExecuteNonQuery();
                cm.Dispose();
                Program.con.Close();
            }
        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.Message);
        }

    }

When I try to register that field in the database it shows me the error

  

Error converting DBNull

This error sometimes appears to me and sometimes it does not ... How can I correct it. This is the exception:

Excepción producida: "System.InvalidCastException" en mscorlib.dll ("No se puede convertir un objeto DBNull en otros tipos.")   System.InvalidCastException