@Override
    protected Object execute(Object data, State state) {
        //will not occur
        return null;
    }
Executor class for Siddhi event attribute that produces multiple values.
This executor is used to extract multiple attribute values as a list from
{@link ComplexEvent}.
modules/siddhi-core/src/main/java/io/siddhi/core/executor/MultiValueVariableFunctionExecutor.java