How to catch a null_pointer_exception?

[catalin8 (Catalin Vulcan)]

On a reindex operation I'm using

if(ctx._source.containsKey("author")) {
    ctx._source.title = ctx._source.title + ctx._source.author[0];
    ctx._source.remove("author");
}

Which throws a null pointer exception error:

"lang":"painless","caused_by":{"type":"null_pointer_exception","reason":null}},"status":400}

How can I check which document causes this error? Because I made sure the author field exists, is an array, and the 0 index exists, so I have no idea why I still get the null pointer exception

[Marius_Dragomir]

What versions are you working with? You might have documents without the _source field. Easiest way to check and fix if that's the case is to wrap it all in another IF clause that checks for the _source field before everything.

[catalin8 (Catalin Vulcan)]

I'm using Elasticsearch 7.6 and ctx._source always works. But for some reason not when performing a reindex operation.

What I did as a result was to use a query to check if the field exists in the source index.