### Question:
StringUtils { public static boolean isEmpty(CharSequence cs) { return cs == null || cs.length() == 0; }  static boolean isEmpty(CharSequence cs); static boolean isNotEmpty(CharSequence cs); static boolean isBlank(CharSequence cs); static boolean isNotBlank(CharSequence cs); static String defaultString(final Object str); static String toString(Object o, String defaultVal); static String toString(Object o); static final String EMPTY; }### Answer:
@Test public void isEmpty() { Assert.assertTrue(StringUtils.isEmpty(null)); Assert.assertTrue(StringUtils.isEmpty("")); Assert.assertFalse(StringUtils.isEmpty(" ")); }