If your Java dev is using Jackson to serialize to JSON, they might not be very experienced with Jackson, or they might think that a Java object with a null field would serialize to JSON with that field omitted. And on another project that might have been true, because Jackson can be configured globally to omit null properties. They can also fix this issue with annotations at the class/field level, most likely .
More details: https://www.baeldung.com/jackson-ignore-null-fields
It’s largely the first one, at least according to The Man Who Killed Google Search.
See also the Hackernews discussion and this follow-up article by the same author (with links to an article with Google’s response, summaries of other discussions on the topic, etc.)