diff --git a/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/ExtractBatchableExternalFunctionCallsRule.java b/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/ExtractBatchableExternalFunctionCallsRule.java
index 1e5d805..54a1bb7 100644
--- a/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/ExtractBatchableExternalFunctionCallsRule.java
+++ b/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/ExtractBatchableExternalFunctionCallsRule.java
@@ -190,13 +190,11 @@
             if (!assignVars.isEmpty()) {
                 usedVarList.clear();
                 expr.getUsedVariables(usedVarList);
-                for (int i = 0, ln = assignVars.size(); i < ln; i++) {
-                    List<LogicalVariable> candidateVarList = assignVars.get(i);
-                    if (OperatorPropertiesUtil.disjoint(candidateVarList, usedVarList)) {
-                        assignVarList = candidateVarList;
-                        assignExprList = assignExprs.get(i);
-                        break;
-                    }
+                int candidateVarListIdx = assignVars.size() - 1;
+                List<LogicalVariable> candidateVarList = assignVars.get(candidateVarListIdx);
+                if (OperatorPropertiesUtil.disjoint(candidateVarList, usedVarList)) {
+                    assignVarList = candidateVarList;
+                    assignExprList = assignExprs.get(candidateVarListIdx);
                 }
             }
 
diff --git a/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/IntroduceDynamicTypeCastForExternalFunctionRule.java b/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/IntroduceDynamicTypeCastForExternalFunctionRule.java
index 2c5a07d..22d87ac 100644
--- a/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/IntroduceDynamicTypeCastForExternalFunctionRule.java
+++ b/asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/IntroduceDynamicTypeCastForExternalFunctionRule.java
@@ -22,6 +22,7 @@
 import org.apache.asterix.om.functions.BuiltinFunctions;
 import org.apache.asterix.om.functions.ExternalFunctionInfo;
 import org.apache.asterix.om.typecomputer.base.TypeCastUtils;
+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.AUnionType;
@@ -82,6 +83,9 @@
             if (reqArgType.getTypeTag() == ATypeTag.OBJECT) {
                 castFlag = !IntroduceDynamicTypeCastRule.compatible((ARecordType) reqArgType, inputType,
                         argExpr.getValue().getSourceLocation());
+            } else if (reqArgType.getTypeTag() == ATypeTag.ANY) {
+                IAType inputPrimeType = TypeComputeUtils.getActualType(inputType);
+                castFlag = inputPrimeType.getTypeTag().isDerivedType();
             } else {
                 castFlag = !reqArgType.equals(inputType);
             }
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/toplevel_fn/mysentiment.0.ddl.sqlpp b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/toplevel_fn/toplevel_fn.0.ddl.sqlpp
similarity index 100%
rename from asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/toplevel_fn/mysentiment.0.ddl.sqlpp
rename to asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/toplevel_fn/toplevel_fn.0.ddl.sqlpp
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/toplevel_fn/mysentiment.1.lib.sqlpp b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/toplevel_fn/toplevel_fn.1.lib.sqlpp
similarity index 100%
rename from asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/toplevel_fn/mysentiment.1.lib.sqlpp
rename to asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/toplevel_fn/toplevel_fn.1.lib.sqlpp
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/toplevel_fn/mysentiment.2.ddl.sqlpp b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/toplevel_fn/toplevel_fn.2.ddl.sqlpp
similarity index 100%
rename from asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/toplevel_fn/mysentiment.2.ddl.sqlpp
rename to asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/toplevel_fn/toplevel_fn.2.ddl.sqlpp
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/toplevel_fn/mysentiment.3.query.sqlpp b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/toplevel_fn/toplevel_fn.3.query.sqlpp
similarity index 100%
rename from asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/toplevel_fn/mysentiment.3.query.sqlpp
rename to asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/toplevel_fn/toplevel_fn.3.query.sqlpp
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/toplevel_fn/toplevel_fn.4.query.sqlpp b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/toplevel_fn/toplevel_fn.4.query.sqlpp
new file mode 100644
index 0000000..7ebfc7a
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/toplevel_fn/toplevel_fn.4.query.sqlpp
@@ -0,0 +1,27 @@
+/*
+ * 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.
+ */
+
+/*
+ * Testcase for ASTERIXDB-2884
+ */
+
+use externallibtest;
+
+sqrt(sqrt(null));
+
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/toplevel_fn/mysentiment.4.ddl.sqlpp b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/toplevel_fn/toplevel_fn.5.ddl.sqlpp
similarity index 100%
rename from asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/toplevel_fn/mysentiment.4.ddl.sqlpp
rename to asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/toplevel_fn/toplevel_fn.5.ddl.sqlpp
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/results/external-library/toplevel_fn/toplevel_fn.1.adm b/asterixdb/asterix-app/src/test/resources/runtimets/results/external-library/toplevel_fn/toplevel_fn.3.adm
similarity index 100%
rename from asterixdb/asterix-app/src/test/resources/runtimets/results/external-library/toplevel_fn/toplevel_fn.1.adm
rename to asterixdb/asterix-app/src/test/resources/runtimets/results/external-library/toplevel_fn/toplevel_fn.3.adm
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/results/external-library/toplevel_fn/toplevel_fn.4.adm b/asterixdb/asterix-app/src/test/resources/runtimets/results/external-library/toplevel_fn/toplevel_fn.4.adm
new file mode 100644
index 0000000..ec747fa
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/results/external-library/toplevel_fn/toplevel_fn.4.adm
@@ -0,0 +1 @@
+null
\ No newline at end of file