### Question:
CharSequenceUtil { public static boolean isEmpty(CharSequence charSequence) { return charSequence == null || charSequence.length() == 0; }  static boolean isEmpty(CharSequence charSequence); static boolean isNotEmpty(CharSequence charSequence); static boolean isBlank(CharSequence charSequence); static boolean isNotBlank(CharSequence charSequence);  }### Answer:
@Test public void testIsEmpty() { assertTrue(CharSequenceUtil.isEmpty(null)); assertTrue(CharSequenceUtil.isEmpty("")); assertFalse(CharSequenceUtil.isEmpty(" ")); assertFalse(CharSequenceUtil.isEmpty(" \t\n\r ")); assertFalse(CharSequenceUtil.isEmpty("a")); assertFalse(CharSequenceUtil.isEmpty(" a ")); }