private void saveMap(Map<Address, Saveable> map,
			ObjectPropertyMap<? extends Saveable> propertyMap) {
		Set<Entry<Address, Saveable>> entrySet = map.entrySet();
		for (Entry<Address, Saveable> entry : entrySet) {
			Address key = entry.getKey();
			Saveable value = entry.getValue();

			if (value instanceof LazySaveableXML) {
				if (((LazySaveableXML) value).isEmpty()) {
					// don't save empty data
					continue;
				}
			}

			if (value != null) {
				propertyMap.add(key, value);
			}
			else {
				propertyMap.remove(key);
			}
		}
	}
Note: this method does not clear group vertex locations.
@param functionGraph function graph
Ghidra/Features/FunctionGraph/src/main/java/ghidra/app/plugin/core/functiongraph/mvc/FunctionGraphVertexAttributes.java