code: @SuppressWarnings("unchecked")
    public <K, V> Map<K, V> get(PropertyMapKey<K, V> property) {
      if (contains(property)) {
        return (Map<K, V>) properties.get(property.getName());
      } else {
        return new HashMap<K, V>();
      }
    }
docs: Returns the map to which the specified property key is mapped, or
  an empty map if this properties contains no mapping for the property key.
  Note that the empty map is not mapped to the property key.
  
  @param property
  the property key whose associated map is to be returned
  @return the map to which the specified property key is mapped, or
  an empty map if this properties contains no mapping for the property key
  
  @see #putMapEntry(PropertyMapKey, Object, Object)