Return empty optional if value is null

[Febell]

If we return an optional and the first element of the list exists but the value is null the optional throws an exception like:

java.lang.NullPointerException: null
	at java.base/java.util.Objects.requireNonNull(Objects.java:233)
	at java.base/java.util.Optional.of(Optional.java:113)

So we should return an empty optional if the first element of the list exists but the value is null.

[zach-m]

A list with null value should not happen. We need to fix the source of the problem.
Can you provide an example when this happens?
It seems that a better approach would be to prevent adding nulls to the list when it is initialized.

[Febell]

Sure I can do that. I attached a file with a real life ONIX file stripped down to the trouble causing book:

GTUPD00139360.XML

You can cause the error by calling:

try (InputStream inputStream = Files.newInputStream(Path.of("GTUPD00139360.XML"))) {
   List<JonixRecord> records = Jonix.source(inputStream).stream().toList();
   for (JonixRecord record : records) {
     Jonix.toBaseProduct(record);
   }
}

The exception I get is located at the code-line for:

dest.editionType = product.editionTypeCodes().firstValue().orElse(null);

Hope that helps. Sorry that I can not pinpoint it more, but I not familiar enough with ONIX to find it.