@Override
        public Object apply(final String s, final GremlinParser.VariableContext variableContext) {
            if (!variables.containsKey(s)) {
                throw new VariableResolverException(String.format("No variable found for %s", s));
            }

            return variables.get(s);
        }
Allows for a provided variable set in the form of a {@code Map}, where the keys are variable names and the
values are the parameter values to be injected into the traversal in their place.
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/language/grammar/VariableResolver.java