code: public void addItem(String key, PdfNumber n) {
  		PdfName fieldname = new PdfName(key);
  		PdfCollectionField field = (PdfCollectionField)schema.get(fieldname);
  		if (field.fieldType == PdfCollectionField.NUMBER) {
  			put(fieldname, n);
  		}
  	}
docs: Sets the value of the collection item.
  @param n