public void setDefault(String key, String value) {
    String s = properties.getProperty(key);
    if (StringUtils.isBlank(s)) {
      properties.setProperty(key, value);
    }
  }
@Test
  public void setDefault() {
    Properties p = new Properties();
    p.setProperty("foo", "foo_value");
    Props props = new Props(p);
    props.setDefault("foo", "foo_def");
    props.setDefault("bar", "bar_def");

    assertThat(props.value("foo")).isEqualTo("foo_value");
    assertThat(props.value("bar")).isEqualTo("bar_def");
    assertThat(props.value("other")).isNull();
  }