private boolean probe(File modelFile) {
        try {
            BufferedReader reader = IOUtils.createReader(modelFile.getAbsolutePath());
            String line;
            while ((line = reader.readLine()) != null) {
                line = line.trim();
                if (line.startsWith("[")) return true;
                if ( ! line.isEmpty()) return false;
            }
            return false;
        }
        catch (IOException e) {
            throw new IllegalArgumentException("Could not read '" + modelFile + "'", e);
        }
    }
Returns true if the give file looks like an XGBoost json file.
Currently, we just check if the file has an array on the top level.
model-integration/src/main/java/ai/vespa/rankingexpression/importer/xgboost/XGBoostImporter.java