public synchronized void saveCustomPropertiesTo(File file){
  if (file == null)   throw new NullPointerException("File cannot be null");
  if (file.isDirectory())   throw new IllegalArgumentException("Not a valid file: " + file);
  Properties prop=getCustomProperties(false);
  if (prop != null && !prop.isEmpty())   storeProperties(prop,file);
}

public synchronized void saveCustomPropertiesTo ( File file ) { if ( file == null ) throw new NullPointerException ( "File cannot be null" ) ; if ( file . isDirectory ( ) ) throw new IllegalArgumentException ( "Not a valid file: " + file ) ; Properties prop = getCustomProperties ( false ) ; if ( prop != null && ! prop . isEmpty ( ) ) storeProperties ( prop , file ) ; }
saves persistent custom properties to a file .
