diff --git a/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/am/AbstractIntroduceAccessMethodRule.java b/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/am/AbstractIntroduceAccessMethodRule.java
index f4178d7..4f9b4df 100644
--- a/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/am/AbstractIntroduceAccessMethodRule.java
+++ b/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/am/AbstractIntroduceAccessMethodRule.java
@@ -30,6 +30,8 @@
 
 import org.apache.asterix.common.config.DatasetConfig.DatasetType;
 import org.apache.asterix.common.config.DatasetConfig.IndexType;
+import org.apache.asterix.common.exceptions.CompilationException;
+import org.apache.asterix.common.exceptions.ErrorCode;
 import org.apache.asterix.dataflow.data.common.ExpressionTypeComputer;
 import org.apache.asterix.metadata.declared.MetadataProvider;
 import org.apache.asterix.metadata.entities.Index;
@@ -38,6 +40,7 @@
 import org.apache.asterix.om.base.AString;
 import org.apache.asterix.om.constants.AsterixConstantValue;
 import org.apache.asterix.om.functions.BuiltinFunctions;
+import org.apache.asterix.om.typecomputer.impl.TypeComputeUtils;
 import org.apache.asterix.om.types.ARecordType;
 import org.apache.asterix.om.types.ATypeTag;
 import org.apache.asterix.om.types.AbstractCollectionType;
@@ -872,9 +875,15 @@
                 }
 
                 if (!isByName) {
-                    fieldName = sourceVar.equals(metaVar)
-                            ? ((ARecordType) metaType.getSubFieldType(parentFieldNames)).getFieldNames()[fieldIndex]
-                            : ((ARecordType) recordType.getSubFieldType(parentFieldNames)).getFieldNames()[fieldIndex];
+                    IAType subFieldType = sourceVar.equals(metaVar) ? metaType.getSubFieldType(parentFieldNames)
+                            : recordType.getSubFieldType(parentFieldNames);
+                    // Sub-field type can be AUnionType in case if it's optional. Thus, needs to get the actual type.
+                    subFieldType = TypeComputeUtils.getActualType(subFieldType);
+                    if (subFieldType.getTypeTag() != ATypeTag.OBJECT) {
+                        throw CompilationException.create(ErrorCode.TYPE_CONVERT, subFieldType,
+                                ARecordType.class.getName());
+                    }
+                    fieldName = ((ARecordType) subFieldType).getFieldNames()[fieldIndex];
                 }
                 if (optFuncExpr != null) {
                     optFuncExpr.setSourceVar(funcVarIndex, ((AssignOperator) op).getVariables().get(assignVarIndex));
diff --git a/asterixdb/asterix-app/src/test/resources/optimizerts/queries/filter/inverted-btree-search-return-optional-field.sqlpp b/asterixdb/asterix-app/src/test/resources/optimizerts/queries/filter/inverted-btree-search-return-optional-field.sqlpp
new file mode 100644
index 0000000..3221cc3
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/optimizerts/queries/filter/inverted-btree-search-return-optional-field.sqlpp
@@ -0,0 +1,91 @@
+/*
+ * 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.
+ */
+
+drop dataverse twitter if exists;
+create dataverse twitter if not exists;
+use twitter;
+
+create type typeUser if not exists as open {
+    id: int64,
+    name: string,
+    screen_name : string,
+    profile_image_url : string?,
+    lang : string,
+    location: string,
+    create_at: date,
+    description: string,
+    followers_count: int32,
+    friends_count: int32,
+    statues_count: int64
+};
+
+create type typePlace if not exists as open{
+    country : string,
+    country_code : string,
+    full_name : string,
+    id : string,
+    name : string,
+    place_type : string,
+    bounding_box : rectangle
+};
+
+create type typeGeoTag if not exists as open {
+    stateID: int32,
+    stateName: string,
+    countyID: int32,
+    countyName: string,
+    cityID: int32?,
+    cityName: string?
+};
+
+create type typeTweet if not exists as open {
+    create_at : datetime,
+    id: int64,
+    text: string,
+    in_reply_to_status : int64,
+    in_reply_to_user : int64,
+    favorite_count : int64,
+    coordinate: point?,
+    retweet_count : int64,
+    lang : string,
+    is_retweet: boolean,
+    hashtags : {{ string }} ?,
+    user_mentions : {{ int64 }} ? ,
+    user : typeUser,
+    place : typePlace?,
+    geo_tag: typeGeoTag
+};
+
+create dataset ds_tweet(typeTweet) if not exists primary key id with filter on create_at with
+{"merge-policy":
+  {"name":"prefix","parameters":
+    {"max-mergable-component-size":134217728, "max-tolerance-component-count":10}
+  }
+};
+
+create index text_idx if not exists on ds_tweet(text) type fulltext;
+
+select t.`place`.`bounding_box` as `place.bounding_box`,t.`user`.`id` as `user.id`,t.`id` as `id`,
+       t.`coordinate` as `coordinate`,t.`create_at` as `create_at`
+from twitter.ds_tweet t
+where t.`create_at` >= datetime('2018-02-22T10:53:07.888Z') and t.`create_at` < datetime('2018-02-22T18:50:39.301Z')
+      and ftcontains(t.`text`, ['francisco'], {'mode':'all'}) and t.`geo_tag`.`stateID` in [ 37,51,24,11 ]
+order by t.`create_at` desc
+limit 2147483647
+offset 0;
diff --git a/asterixdb/asterix-app/src/test/resources/optimizerts/results/filter/inverted-btree-search-return-optional-field.plan b/asterixdb/asterix-app/src/test/resources/optimizerts/results/filter/inverted-btree-search-return-optional-field.plan
new file mode 100644
index 0000000..629a05a
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/optimizerts/results/filter/inverted-btree-search-return-optional-field.plan
@@ -0,0 +1,43 @@
+-- DISTRIBUTE_RESULT  |UNPARTITIONED|
+  -- ONE_TO_ONE_EXCHANGE  |UNPARTITIONED|
+    -- STREAM_LIMIT  |UNPARTITIONED|
+      -- STREAM_PROJECT  |PARTITIONED|
+        -- ASSIGN  |PARTITIONED|
+          -- SORT_MERGE_EXCHANGE [$$37(DESC) ]  |PARTITIONED|
+            -- STREAM_LIMIT  |PARTITIONED|
+              -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+                -- STABLE_SORT [topK: 2147483647] [$$37(DESC)]  |PARTITIONED|
+                  -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+                    -- STREAM_PROJECT  |PARTITIONED|
+                      -- STREAM_SELECT  |PARTITIONED|
+                        -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+                          -- PRE_CLUSTERED_GROUP_BY[$$38]  |PARTITIONED|
+                                  {
+                                    -- AGGREGATE  |LOCAL|
+                                      -- STREAM_SELECT  |LOCAL|
+                                        -- NESTED_TUPLE_SOURCE  |LOCAL|
+                                  }
+                            -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+                              -- STABLE_SORT [$$38(ASC)]  |PARTITIONED|
+                                -- HASH_PARTITION_EXCHANGE [$$38]  |PARTITIONED|
+                                  -- STREAM_PROJECT  |PARTITIONED|
+                                    -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+                                      -- HYBRID_HASH_JOIN [$$39][$#1]  |PARTITIONED|
+                                        -- HASH_PARTITION_EXCHANGE [$$39]  |PARTITIONED|
+                                          -- STREAM_PROJECT  |PARTITIONED|
+                                            -- ASSIGN  |PARTITIONED|
+                                              -- STREAM_SELECT  |PARTITIONED|
+                                                -- ASSIGN  |PARTITIONED|
+                                                  -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+                                                    -- BTREE_SEARCH  |PARTITIONED|
+                                                      -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+                                                        -- STABLE_SORT [$$52(ASC)]  |PARTITIONED|
+                                                          -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+                                                            -- SINGLE_PARTITION_INVERTED_INDEX_SEARCH  |PARTITIONED|
+                                                              -- ONE_TO_ONE_EXCHANGE  |PARTITIONED|
+                                                                -- ASSIGN  |PARTITIONED|
+                                                                  -- EMPTY_TUPLE_SOURCE  |PARTITIONED|
+                                        -- HASH_PARTITION_EXCHANGE [$#1]  |PARTITIONED|
+                                          -- ASSIGN  |UNPARTITIONED|
+                                            -- UNNEST  |UNPARTITIONED|
+                                              -- EMPTY_TUPLE_SOURCE  |UNPARTITIONED|