fix: ORDER BY window definition should work on null (#8444)

Author: viirya

datafusion/optimizer/src/analyzer/type_coercion.rs

@@ -503,7 +503,10 @@ fn coerce_window_frame(
     let target_type = match window_frame.units {
         WindowFrameUnits::Range => {
             if let Some(col_type) = current_types.first() {
-                if col_type.is_numeric() || is_utf8_or_large_utf8(col_type) {
+                if col_type.is_numeric()
+                    || is_utf8_or_large_utf8(col_type)
+                    || matches!(col_type, DataType::Null)
+                {
                     col_type
                 } else if is_datetime(col_type) {
                     &DataType::Interval(IntervalUnit::MonthDayNano)

datafusion/sqllogictest/test_files/window.slt

@@ -3785,3 +3785,11 @@ select a,
 ----
 1 1
 2 1
+
+query II
+select a,
+       rank() over (order by null RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) rnk
+       from (select 1 a union select 2 a) q ORDER BY a
+----
+1 1
+2 1