Fix migration guide

Author: iRakson

docs/sql-migration-guide.md

@@ -216,9 +216,7 @@ license: |
 
   - Since Spark 3.0, the `size` function returns `NULL` for the `NULL` input. In Spark version 2.4 and earlier, this function gives `-1` for the same input. To restore the behavior before Spark 3.0, you can set `spark.sql.legacy.sizeOfNull` to `true`.
 
-  - Since Spark 3.0, when the `array` function is called without any parameters, it returns an empty array of `NullType`. In Spark version 2.4 and earlier, it returns an empty array of string type. To restore the behavior before Spark 3.0, you can set `spark.sql.legacy.createEmptyCollectionUsingStringType.enabled` to `true`.
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-  - Since Spark 3.0, when the `map` function is called without any parameters, it returns an empty map with `NullType` as key/value type. In Spark version 2.4 and earlier, it returns an empty map of string type. To restore the behavior before Spark 3.0, you can set `spark.sql.legacy.createEmptyCollectionUsingStringType.enabled` to `true`.
+  - Since Spark 3.0, when the `array`/`map` function is called without any parameters, it returns an empty collection with `NullType` as element type. In Spark version 2.4 and earlier, it returns an empty collection with `StringType` as element type. To restore the behavior before Spark 3.0, you can set `spark.sql.legacy.createEmptyCollectionUsingStringType.enabled` to `true`.
 
   - Since Spark 3.0, the interval literal syntax does not allow multiple from-to units anymore. For example, `SELECT INTERVAL '1-1' YEAR TO MONTH '2-2' YEAR TO MONTH'` throws parser exception.