pepijnve commented on PR #25023:
URL: https://github.com/apache/datafusion/pull/25023#issuecomment-5572936030

   > I think it was introduced in [PR 
#19955](https://github.com/apache/datafusion/pull/19955) and was DataFusion 53 
breaking change because unrelated structs could otherwise silently lose data. 
For example, casting {left: 1} to {alpha: INT NULL} would discard left and 
produce {alpha: NULL}. The nullability check only protects nonnullable target 
fields, so it cannot replace the overlap check.
   
   Thanks for the pointer to the PR. The comment made by @adriangb that this 
matches DuckDB behaviour makes sense, and as you said, coming from an empty 
struct there's no information to lose anyway. I'll have a go at revising the 
doc comment.


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