private static List<TreeNode> asForest(List<TreeNode> in) {
        List<TreeNode> out = new ArrayList<>(in.size());
        for (TreeNode node : in) {
            if (node instanceof FeatureNode) {
                out.add(node);
            } else if (node instanceof ResponseNode) { // TODO): We should stop this sillyness ...
                out.add(new NumericFeatureNode("value(0)", new DoubleValue(1), node.samples(), node,
                                                           new ResponseNode(0, Optional.of(0))));
            } else {
                throw new UnsupportedOperationException(node.getClass().getName());
            }
        }
        return Collections.unmodifiableList(out);
    }
Return whether this model has sample information.
Don't bother to check every node as files either has this for all nodes or for none.
searchlib/src/main/java/com/yahoo/searchlib/gbdt/GbdtModel.java