fix

src/AggregateFunctions/AggregateFunctionFactory.cpp

@@ -92,8 +92,10 @@ AggregateFunctionPtr AggregateFunctionFactory::get(
 
         // Pure window functions are not real aggregate functions. Applying
         // combinators doesn't make sense for them, they must handle the
-        // nullability themselves.
-        if (nested_function->asWindowFunction())
+        // nullability themselves. Another special case is functions from Nothing
+        // that are rewritten to AggregateFunctionNothing, in this case
+        // nested_function is nullptr.
+        if (nested_function && nested_function->asWindowFunction())
         {
             return nested_function;
         }

tests/queries/0_stateless/01591_window_functions.reference

@@ -1058,6 +1058,8 @@ settings max_block_size = 3;
 select lagInFrame(toNullable(1)) over ();
 0
 select lagInFrameOrNull(1) over (); -- { serverError 36 }
+select intDiv(1, NULL) x, toTypeName(x), max(x) over ();
+\N	Nullable(Nothing)	\N
 -- case-insensitive SQL-standard synonyms for any and anyLast
 select
     number,

tests/queries/0_stateless/01591_window_functions.sql

@@ -379,6 +379,7 @@ settings max_block_size = 3;
 -- careful with auto-application of Null combinator
 select lagInFrame(toNullable(1)) over ();
 select lagInFrameOrNull(1) over (); -- { serverError 36 }
+select intDiv(1, NULL) x, toTypeName(x), max(x) over ();
 
 -- case-insensitive SQL-standard synonyms for any and anyLast
 select