@Test
void lastOf_boundary_tests() {

    assertEquals("a,b",lastOf("a,b",(String[]) null));
    assertEquals("a,b",lastOf("a,b",""));
    assertEquals("b",lastOf("a,b",","));
    assertEquals("a,b",lastOf("a,b",(String) null));
    assertEquals("", lastOf("a."));
    assertEquals("a",lastOf(".a"));
    assertEquals("", lastOf(null));
}