Changes

    local previous_cell = self._data_rows[i][column]

    local previous_cell = self._data_rows[i][column]

     if previous_cell then

     if previous_cell then

        if row_values[column].values.node == previous_cell.values.node then

        if row_values[column].values.node == previous_cell.values.node and row_values[column].values.time == previous_cell.values.time then

        previous_cell.rowspan = previous_cell.rowspan + 1

        previous_cell.rowspan = previous_cell.rowspan + 1

        row_values[column] = nil

        row_values[column] = nil