NOCOMMIT

We need to decide something important before mering.

Author: nik9000

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/expression/function/scalar/date/DateDiff.java

@@ -167,7 +167,7 @@ public static Part resolve(String dateTimeUnit) {
             """, file = "date", tag = "evalDateDiffYearForDocs"), @Example(description = """
             If any column is multivalued, this will return a `null` result.
             """, file = "date", tag = "date-diff-mv") }
-    )
+    ) // NOCOMMIT can we reserve the right to change the null-and-warn behavior?
     public DateDiff(
         Source source,
         @Param(name = "unit", type = { "keyword", "text" }, description = "Time difference unit") Expression unit,