public static String substVars(String val, PropertyContainer pc1) {
    return substVars(val, pc1, null);
  }
@Test
  public void defaultValueReferencingAVariable() {
    context.putProperty("v1", "k1");
    String result = OptionHelper.substVars("${undef:-${v1}}", context);
    assertEquals("k1", result);
  }