public WalkResult evaluate(ParseTree tree, String key, String value) {
        if (verbose) {
            LOG.info("===========================================");
            LOG.info("Evaluate: {} => {}", key, value);
            LOG.info("Pattern : {}", requiredPatternText);
            LOG.info("WalkList: {}", walkList);
        }
        WalkResult result = walkList.walk(tree, value);
        if (verbose) {
            LOG.info("Evaluate: Result = {}", result == null ? "null" : result.getValue());
        }
        return result;
    }
@return The fixed value in case of a fixed value. NULL if a dynamic value
analyzer/src/main/java/nl/basjes/parse/useragent/analyze/treewalker/TreeExpressionEvaluator.java