The Signature for ConcatWs in Spark SQL Docs Is Inconsistent with the Actual Behavior

In https://spark.apache.org/docs/latest/api/sql/index.html#concat_ws, the signature of concat_ws is concat_ws(sep, [str | array(str)]+). However, it doesn't actually need any str or array(str) arguments. Only having the sep argument seems to work.

For example, `select concat_ws("a")` returns an empty string.

scala> sql("""select concat_ws("a")""").show
+------------+
|concat_ws(a)|
+------------+
|            |
+------------+