assertEquals("apple - banana - cherry", result);
    }

    @Test
    @DisplayName("Should handle null delimiter by inserting 'null' string")
    void testJoinWithNullDelimiter() {
        String result = StringUtil.join(null, "first", "second", "third");
        assertEquals("firstnullsecondnullthird", result);
    }

    @Test
    @DisplayName("Should handle null elements in array")