code: @GwtIncompatible("java.util.Properties")
    public static ImmutableMap<String, String> fromProperties(
        Properties properties) {
      ImmutableMap.Builder<String, String> builder = ImmutableMap.builder();
  
      for (Enumeration<?> e = properties.propertyNames(); e.hasMoreElements();) {
        String key = (String) e.nextElement();
        builder.put(key, properties.getProperty(key));
      }
  
      return builder.build();
    }
docs: Creates an {@code ImmutableMap<String, String>} from a {@code Properties}
  instance. Properties normally derive from {@code Map<Object, Object>}, but
  they typically contain strings, which is awkward. This method lets you get
  a plain-old-{@code Map} out of a {@code Properties}.
  
  @param properties a {@code Properties} object to be converted
  @return an immutable map containing all the entries in {@code properties}
  @throws ClassCastException if any key in {@code Properties} is not a {@code
  String}
  @throws NullPointerException if any key or value in {@code Properties} is
  null