@Test
void get() {

    assertThrows(NullPointerException.class, () -> instance.get((String) null));
    assertFalse(instance.get("nonExistentDbms").isPresent());
    instance.put("dbms", "password".toCharArray());
    assertTrue(instance.get("dbms").isPresent());
    instance.put("dbms", null);
    assertFalse(instance.get("dbms").isPresent());
}