`Properties#store(OutputStream)` doesn't flush the output to the `OutputStream`

[gastaldi]

The following test fails:

    @Test
    void testStoreOutputStream() throws IOException, URISyntaxException {
        Path f = getResource("/test.properties");
        Properties p = Properties.loadProperties(f);
        ByteArrayOutputStream os = new ByteArrayOutputStream();
        p.store(os);
        assertThat(os.toString()).isEqualTo(readAll(f));
    }

Probably the OutputStreamWriter isn't flushing to the underlying OutputStream?