@SuppressWarnings("SameReturnValue")
            private String visitLookupsFailOnFixedString(ParseTree matcherTree) {
                String value = visit(matcherTree);
                if (value == null) {
                    return null;
                }
                // Now we know this is a fixed value lookup ... JUST DON'T as it is needless.
                throw new InvalidParserConfigurationException("A lookup for a fixed input value is a needless complexity.");
            }
@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