code: public static String getPackageName(Class<?> clazz) {
  		Assert.notNull(clazz, "Class must not be null");
  		return getPackageName(clazz.getName());
  	}
docs: Determine the name of the package of the given class,
  e.g. "java.lang" for the {@code java.lang.String} class.
  @param clazz the class
  @return the package name, or the empty String if the class
  is defined in the default package