code: public void addProperty(String name, Object value) {
          if (value != null) {
              properties.put(name, value);
          } else {
              removeProperty(name);
          }
      }
docs: Adds an optional property to this object.
  If null, any property with the given name will be removed.
  If the property already exists, this new value will replace the old value.
  
  @param name the name of the property
  @param value the value of the property; must be JSON-serializable if not-null