Scriptella: How to handle the error while fetching data from XML through Xpath

i have one query regarding data fetching from XML xpath.

 <query connection-id="in">
    CommunicationCenter/Response/MenuData/Menu/Noun
<!--something I have to do inside script using the data fetched from xpath-->
</query>

My question is - suppose 1 of the XML doesn't have this structure of Xpath. It has "OtherCommCenter/MenuData/Menu/Noun" or something else structure. Then, when I run the job, it says the job is executed with no exception & as it does not get any value from xpath, nothing is happened. Means it gives back null. So, how do I catch the error there? I have to know which element in xpath creates the problem or if that is not possible, at least which xml is creating this error in structure ?

(because in my project, there are multiple XMLs I have to handle & I am doing that by submitting jobs to ExecutorService like you described in How to ETL multiple files using Scriptella?)

P.S. for the last part, I am doing like this

<connection id="in" driver="xpath" url="$input"/>

where "input" is the map key for the different xml file name.

can anybody help me? it is necessary to know asap for my project.

Solution

Here is an artificial example. Let's say there are kind of XMLs - people and cars.

people.xml:

<people>
    <person></person>
</people>

Cars.xml:

<cars>
    <car/>
</car>

The following xml runs 2 queries for /people/person and /cars/car and set global flags if at least one record was found:

<etl>
    <connection driver="jexl" id="jexl"/>
    <connection driver="xpath" id="xpath" url="input.xml"/>
    <connection id="log" driver="text"/>

    <query connection-id="xpath">
        /people/person
        <script connection-id="jexl">
            # set flag to true if at least one element was found
            etl.globals['people']=true;
        </script>
    </query>
    <script connection-id="log" if="!etl.globals['people']">
        WARNING: No people found in the XML file
    </script>

    <query connection-id="xpath">
        /cars/car
        <script connection-id="jexl">
            etl.globals['cars']=true;
        </script>
    </query>

    <script connection-id="log" if="!etl.globals['cars']">
        WARNING: No cars found in the XML file
    </script>
</etl>