code: public void addProperty(String propertyName, Object value)
      {
          if (propertyName != null)
          {
              propertyNames.add(propertyName);
              if (value == null)
              {
                  properties.remove(propertyName);
              }
              else
              {
                  properties.put(propertyName, value);
              }
          }
      }
docs: The name of the property to add. if it already exists, the value is updated. If the propertyname is null,
  the property addition is ignored.
  @param propertyName the name of the property to add
  @param value the value to assign to the given property.