@Override
    protected Object execute(Object[] data, State state) {
        if (data[0] == null) {
            return data[1];
        } else {
            return data[0];
        }
    }
Executor class for default function. Function execution sets the default value assigned by the user when attribute
value is null.
modules/siddhi-core/src/main/java/io/siddhi/core/executor/function/DefaultFunctionExecutor.java