public String get(String key, String defaultValue) {
        String v = get(key);
        if (v == null)    v = defaultValue;
        return v;
    }
@Test
    public void caseInsensitive() {
        EnvVars ev = new EnvVars(Map.of("Path", "A:B:C"));
        assertTrue(ev.containsKey("PATH"));
        assertEquals("A:B:C", ev.get("PATH"));
    }