Review comments

Author: kanoshiou

x-pack/plugin/esql/src/internalClusterTest/java/org/elasticsearch/xpack/esql/action/EsqlActionIT.java

@@ -587,6 +587,17 @@ public void testFilterWithNullAndEval() {
         }
     }
 
+    public void testSortWithNull() {
+        try (EsqlQueryResponse results = run("row a = null | sort a")) {
+            logger.info(results);
+            assertEquals(1, getValuesList(results).size());
+            int countIndex = results.columns().indexOf(new ColumnInfoImpl("a", "null"));
+            assertThat(results.columns().stream().map(ColumnInfo::name).toList(), contains("a"));
+            assertThat(results.columns().stream().map(ColumnInfoImpl::type).toList(), contains(DataType.NULL));
+            assertNull(getValuesList(results).getFirst().get(countIndex));
+        }
+    }
+
     public void testStringLength() {
         try (EsqlQueryResponse results = run("from test | eval l = length(color)")) {
             logger.info(results);

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/plan/physical/EstimatesRowSize.java

@@ -85,7 +85,7 @@ public int consumeAllFields(boolean producesUnsortedDocIds) {
             }
             estimatedRowSize = maxEstimatedRowSize = 0;
             needsSortedDocIds = false;
-            return size;
+            return size == 0 ? 1 : size;
         }
 
         @Override

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/planner/LocalExecutionPlanner.java

@@ -374,6 +374,7 @@ private PhysicalOperation planExchangeSource(ExchangeSourceExec exchangeSource,
 
     private PhysicalOperation planTopN(TopNExec topNExec, LocalExecutionPlannerContext context) {
         final Integer rowSize = topNExec.estimatedRowSize();
+        assert rowSize != null && rowSize > 0 : "estimated row size [" + rowSize + "] wasn't set";
         PhysicalOperation source = plan(topNExec.child(), context);
 
         ElementType[] elementTypes = new ElementType[source.layout.numberOfChannels()];