public static String[] split(final String str, final String separatorChars) {
        if (str == null) {
            return null;
        }
        if (isBlank(str)) {
            return EMPTY_ARRAY;
        }
        if (isBlank(separatorChars)) {
            return str.split(" ");
        }
        return str.split(separatorChars);
    }
@Test
    public void split() {
        String str1 = null;
        String separator1 = "*";
        String[] res1 = StringUtil.split(str1, separator1);
        assert res1 == null;

        String str2 = "";
        String separator2 = "*";
        String[] res2 = StringUtil.split(str2, separator2);
        Assert.assertArrayEquals(res2, new String[0]);

        String str3 = "abc def";
        String separator3 = null;
        String[] res3 = StringUtil.split(str3, separator3);
        Assert.assertArrayEquals(res3, new String[]{"abc", "def"});

        String str4 = "abc def";
        String separator4 = " ";
        String[] res4 = StringUtil.split(str4, separator4);
        Assert.assertArrayEquals(res4, new String[]{"abc", "def"});

        String str5 = "ab:cd:ef";
        String separator5 = ":";
        String[] res5 = StringUtil.split(str5, separator5);
        Assert.assertArrayEquals(res5, new String[]{"ab", "cd", "ef"});

    }