code: @Deprecated
    public void readUnknownGroup(final int fieldNumber,
                                 final MessageLite.Builder builder)
        throws IOException {
      // We know that UnknownFieldSet will ignore any ExtensionRegistry so it
      // is safe to pass null here.  (We can't call
      // ExtensionRegistry.getEmptyRegistry() because that would make this
      // class depend on ExtensionRegistry, which is not part of the lite
      // library.)
      readGroup(fieldNumber, builder, null);
    }
docs: Reads a {@code group} field value from the stream and merges it into the
  given {@link UnknownFieldSet}.
  
  @deprecated UnknownFieldSet.Builder now implements MessageLite.Builder, so
  you can just call {@link #readGroup}.