protected void notImplemented(final ParseTree ctx) {
		final String className = (ctx != null)? ctx.getClass().getName() : "";
		throw new UnsupportedOperationException("Method not implemented for context class " + className);
	}
This class provides implementation of {@link GremlinVisitor}, where each method will throw
{@code UnsupportedOperationException}. All the visitor class will extend this class, so that if there is method
that are not manually implemented, and called, an exception will be thrown to help us catch bugs.

@param <T> The return type of the visit operation. Use {@link Void} for
operations with no return type.
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/language/grammar/DefaultGremlinBaseVisitor.java