chore(agg): comment out bad row count panic

src/stream/src/executor/aggregation/agg_group.rs

@@ -310,14 +310,22 @@ impl<S: StateStore, Strtg: Strategy> AggGroup<S, Strtg> {
             self.states[self.row_count_index],
             AggState::Value(ref state) => state
         );
-        let row_count = *row_count_state
+        let mut row_count = *row_count_state
             .as_datum()
             .as_ref()
             .expect("row count state should not be NULL")
             .as_int64();
         if row_count < 0 {
             tracing::error!(group = ?self.group_key_row(), "bad row count");
-            panic!("row count should be non-negative")
+            // panic!("row count should be non-negative") // TODO: need strict mode sys param / session var
+
+            // NOTE: Here is the case that an inconsistent `DELETE` arrives at HashAgg executor, and there's no
+            // corresponding group existing before (or has been deleted). In this case, `prev_row_count()` will
+            // report `0`. To ignore the inconsistent, we set `curr_row_count` to `0` here, so that `OnlyOutputIfHasInput`
+            // will return no change, so that the inconsistent will be hidden from downstream. This won't prevent from
+            // incorrect results of existing groups, but at least can prevent from downstream panicking due to non-existing
+            // keys.
+            row_count = 0;
         }
         row_count.try_into().unwrap()
     }