Remove useless assertion

h2/src/main/org/h2/expression/aggregate/AbstractAggregate.java

@@ -95,7 +95,6 @@ public abstract class AbstractAggregate extends DataAnalysisOperation {
         boolean grouped = frame == null
                 || frame.getUnits() != WindowFrameUnits.ROWS && frame.getExclusion().isGroupOrNoOthers();
         if (frame == null) {
-            assert over.getOrderBy() != null;
             aggregateFastPartition(session, result, ordered, rowIdColumn, grouped);
             return;
         }

h2/src/main/org/h2/expression/analysis/DataAnalysisOperation.java

@@ -411,7 +411,8 @@ public abstract class DataAnalysisOperation extends Expression {
     }
 
     /**
-     * Returns result of this window function or window aggregate.
+     * Returns result of this window function or window aggregate. This method
+     * may not be called on window aggregate without window order clause.
      *
      * @param session
      *            the session