public boolean hasKey(String key) {
        if (null == key) {
            return false;
        }
        return props.containsKey(key);
    }
@Test
    public void testHasKey() {
        Environment environment = Environment.of("classpath:/application.properties");
        assertEquals(Boolean.FALSE, environment.hasKey("hello"));
        assertEquals(Boolean.TRUE, environment.hasKey("app.version"));
        assertEquals(Boolean.FALSE, environment.hasKey(null));
    }