protected Object execute(Object data) {
        S state = stateHolder.getState();
        try {
            return execute(data, state);
        } finally {
            stateHolder.returnState(state);
        }
    }
The main execution method which will be called upon event arrival
when there are zero or one function parameter

@param data null if the function parameter count is zero or
            runtime data value of the function parameter
@return the function result
modules/siddhi-core/src/main/java/io/siddhi/core/executor/function/FunctionExecutor.java