code: public String getProperty(String propertyName)
      {
          ChangeStack<String> stack = properties.get(propertyName);
          if (stack == null)
          {
              return null;
          }
  
          return stack.getCurrentValue();
      }
docs: Retrieve the value associated with the given property.
  
  @param propertyName
  the property whose value is requested
  @return the value associated with the given property or <code>null</code>
  if no such property exists