diff --git a/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/am/OptimizableOperatorSubTree.java b/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/am/OptimizableOperatorSubTree.java
index d45e7f2..c55edf9 100644
--- a/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/am/OptimizableOperatorSubTree.java
+++ b/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/am/OptimizableOperatorSubTree.java
@@ -431,6 +431,7 @@
                 }
                 break;
             case EXTERNAL_SCAN:
+            case COLLECTION_SCAN:
                 break;
             case NO_DATASOURCE:
             default:
diff --git a/asterixdb/asterix-app/src/test/resources/optimizerts/queries/leftouterjoin/query-ASTERIXDB-2988.sqlpp b/asterixdb/asterix-app/src/test/resources/optimizerts/queries/leftouterjoin/query-ASTERIXDB-2988.sqlpp
new file mode 100644
index 0000000..2add75a
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/optimizerts/queries/leftouterjoin/query-ASTERIXDB-2988.sqlpp
@@ -0,0 +1,34 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+/*
+ * No index join because the probe branch does not have a primary key
+ */
+
+DROP dataverse test if exists;
+CREATE dataverse test;
+USE test;
+
+CREATE DATASET ds1(x int, y int) PRIMARY KEY x;
+
+CREATE INDEX idx_y ON ds1(y) TYPE BTREE;
+
+SELECT r1, ds1.x, ds1.y
+FROM range(0, 4) r1 LEFT OUTER JOIN ds1 ON r1 /* +indexnl */ = ds1.y
+ORDER BY r1;
\ No newline at end of file
diff --git a/asterixdb/asterix-app/src/test/resources/optimizerts/results/leftouterjoin/query-ASTERIXDB-2988.plan b/asterixdb/asterix-app/src/test/resources/optimizerts/results/leftouterjoin/query-ASTERIXDB-2988.plan
new file mode 100644
index 0000000..96fbf3a
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/optimizerts/results/leftouterjoin/query-ASTERIXDB-2988.plan
@@ -0,0 +1,20 @@
+-- DISTRIBUTE_RESULT  |PARTITIONED|
+  -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+    -- STREAM_PROJECT  |PARTITIONED|
+      -- ASSIGN  |PARTITIONED|
+        -- SORT_MERGE_EXCHANGE [$$r1(ASC) ]  |PARTITIONED|
+          -- STABLE_SORT [$$r1(ASC)]  |PARTITIONED|
+            -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+              -- STREAM_PROJECT  |PARTITIONED|
+                -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+                  -- HYBRID_HASH_JOIN [$$r1][$$32]  |PARTITIONED|
+                    -- HASH_PARTITION_EXCHANGE [$$r1]  |PARTITIONED|
+                      -- UNNEST  |UNPARTITIONED|
+                        -- EMPTY_TUPLE_SOURCE  |UNPARTITIONED|
+                    -- HASH_PARTITION_EXCHANGE [$$32]  |PARTITIONED|
+                      -- ASSIGN  |PARTITIONED|
+                        -- STREAM_PROJECT  |PARTITIONED|
+                          -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+                            -- DATASOURCE_SCAN (test.ds1)  |PARTITIONED|
+                              -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+                                -- EMPTY_TUPLE_SOURCE  |PARTITIONED|