Please see this documentation page:
https://www.postgresql.org/about/featurematrix/detail/392/
It states, "By default, NULL values are not treated as distinct entries."
It should state, "By default, NULL values are treated as distinct entries."
See this blog
<https://blog.rustprooflabs.com/2022/07/postgres-15-unique-improvement-with-null>
.
Best,
Ian