private void sanityCheck()
{
if (PdfFont == null)
throw new NullReferenceException("`PdfFont` is null.");
if (ContentByte == null)
throw new NullReferenceException("`ContentByte` is null.");
if (Items == null)
throw new NullReferenceException("`Items` is null.");
if (!Items.Any())
throw new InvalidOperationException("There is no BarChartItem to draw.");
}