diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/python_open_type_validation/type_validation.10.query.sqlpp b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/python_open_type_validation/type_validation.10.query.sqlpp
new file mode 100644
index 0000000..69a0b25
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/python_open_type_validation/type_validation.10.query.sqlpp
@@ -0,0 +1,25 @@
+/*
+ * 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.
+ */
+use externallibtest;
+
+set `rewrite_attempt_batch_assign` "false";
+
+typeValidationNullCall(907, 9.07, "907", 9.07, true, unix_time_from_date_in_days(date("2013-01-01")),
+               unix_time_from_datetime_in_secs(datetime("1989-09-07T12:13:14.039Z")), missing);
+
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/python_open_type_validation/type_validation.4.ddl.sqlpp b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/python_open_type_validation/type_validation.11.ddl.sqlpp
similarity index 100%
rename from asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/python_open_type_validation/type_validation.4.ddl.sqlpp
rename to asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/python_open_type_validation/type_validation.11.ddl.sqlpp
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/python_open_type_validation/type_validation.2.ddl.sqlpp b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/python_open_type_validation/type_validation.2.ddl.sqlpp
index a8ba8a1..8041b5e 100644
--- a/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/python_open_type_validation/type_validation.2.ddl.sqlpp
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/python_open_type_validation/type_validation.2.ddl.sqlpp
@@ -18,6 +18,8 @@
  */
 use externallibtest;
 
-create function typeValidation(a, b, c, d, e, f, g)
+create function typeValidation(a, b, c, d, e, f, g, h)
   as "roundtrip", "Tests.roundtrip" at testlib;
 
+create function typeValidationNullCall(a, b, c, d, e, f, g, h)
+  as "roundtrip", "Tests.roundtrip" at testlib with {"null-call": true};
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/python_open_type_validation/type_validation.3.query.sqlpp b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/python_open_type_validation/type_validation.3.query.sqlpp
index 0ae7d0c..f9aaf57 100644
--- a/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/python_open_type_validation/type_validation.3.query.sqlpp
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/python_open_type_validation/type_validation.3.query.sqlpp
@@ -17,6 +17,7 @@
  * under the License.
  */
 use externallibtest;
+
 typeValidation(907, 9.07, "907", 9.07, true, unix_time_from_date_in_days(date("2013-01-01")),
-               unix_time_from_datetime_in_secs(datetime("1989-09-07T12:13:14.039Z")));
+               unix_time_from_datetime_in_secs(datetime("1989-09-07T12:13:14.039Z")), null);
 
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/python_open_type_validation/type_validation.4.query.sqlpp b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/python_open_type_validation/type_validation.4.query.sqlpp
new file mode 100644
index 0000000..884f31f
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/python_open_type_validation/type_validation.4.query.sqlpp
@@ -0,0 +1,25 @@
+/*
+ * 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.
+ */
+use externallibtest;
+
+set `rewrite_attempt_batch_assign` "false";
+
+typeValidation(907, 9.07, "907", 9.07, true, unix_time_from_date_in_days(date("2013-01-01")),
+               unix_time_from_datetime_in_secs(datetime("1989-09-07T12:13:14.039Z")), null);
+
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/python_open_type_validation/type_validation.5.query.sqlpp b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/python_open_type_validation/type_validation.5.query.sqlpp
new file mode 100644
index 0000000..fdd71ef
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/python_open_type_validation/type_validation.5.query.sqlpp
@@ -0,0 +1,23 @@
+/*
+ * 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.
+ */
+use externallibtest;
+
+typeValidationNullCall(907, 9.07, "907", 9.07, true, unix_time_from_date_in_days(date("2013-01-01")),
+               unix_time_from_datetime_in_secs(datetime("1989-09-07T12:13:14.039Z")), null);
+
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/python_open_type_validation/type_validation.6.query.sqlpp b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/python_open_type_validation/type_validation.6.query.sqlpp
new file mode 100644
index 0000000..b85e0d0
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/python_open_type_validation/type_validation.6.query.sqlpp
@@ -0,0 +1,25 @@
+/*
+ * 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.
+ */
+use externallibtest;
+
+set `rewrite_attempt_batch_assign` "false";
+
+typeValidationNullCall(907, 9.07, "907", 9.07, true, unix_time_from_date_in_days(date("2013-01-01")),
+               unix_time_from_datetime_in_secs(datetime("1989-09-07T12:13:14.039Z")), null);
+
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/python_open_type_validation/type_validation.7.query.sqlpp b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/python_open_type_validation/type_validation.7.query.sqlpp
new file mode 100644
index 0000000..fa76f1a
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/python_open_type_validation/type_validation.7.query.sqlpp
@@ -0,0 +1,23 @@
+/*
+ * 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.
+ */
+use externallibtest;
+
+typeValidation(907, 9.07, "907", 9.07, true, unix_time_from_date_in_days(date("2013-01-01")),
+               unix_time_from_datetime_in_secs(datetime("1989-09-07T12:13:14.039Z")), missing);
+
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/python_open_type_validation/type_validation.8.query.sqlpp b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/python_open_type_validation/type_validation.8.query.sqlpp
new file mode 100644
index 0000000..30640fd
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/python_open_type_validation/type_validation.8.query.sqlpp
@@ -0,0 +1,25 @@
+/*
+ * 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.
+ */
+use externallibtest;
+
+set `rewrite_attempt_batch_assign` "false";
+
+typeValidation(907, 9.07, "907", 9.07, true, unix_time_from_date_in_days(date("2013-01-01")),
+               unix_time_from_datetime_in_secs(datetime("1989-09-07T12:13:14.039Z")), missing);
+
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/python_open_type_validation/type_validation.9.query.sqlpp b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/python_open_type_validation/type_validation.9.query.sqlpp
new file mode 100644
index 0000000..810ba3c
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/python_open_type_validation/type_validation.9.query.sqlpp
@@ -0,0 +1,23 @@
+/*
+ * 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.
+ */
+use externallibtest;
+
+typeValidationNullCall(907, 9.07, "907", 9.07, true, unix_time_from_date_in_days(date("2013-01-01")),
+               unix_time_from_datetime_in_secs(datetime("1989-09-07T12:13:14.039Z")), missing);
+
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/results/external-library/python_open_type_validation/type_validation.1.adm b/asterixdb/asterix-app/src/test/resources/runtimets/results/external-library/python_open_type_validation/type_validation.1.adm
index 93f8aec..19765bd 100644
--- a/asterixdb/asterix-app/src/test/resources/runtimets/results/external-library/python_open_type_validation/type_validation.1.adm
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/results/external-library/python_open_type_validation/type_validation.1.adm
@@ -1 +1 @@
-[ 907, 9.07, "907", 9.07, true, 15706, 621173594 ]
+null
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/results/external-library/python_open_type_validation/type_validation.2.adm b/asterixdb/asterix-app/src/test/resources/runtimets/results/external-library/python_open_type_validation/type_validation.2.adm
new file mode 100644
index 0000000..19765bd
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/results/external-library/python_open_type_validation/type_validation.2.adm
@@ -0,0 +1 @@
+null
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/results/external-library/python_open_type_validation/type_validation.3.adm b/asterixdb/asterix-app/src/test/resources/runtimets/results/external-library/python_open_type_validation/type_validation.3.adm
new file mode 100644
index 0000000..53fd925
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/results/external-library/python_open_type_validation/type_validation.3.adm
@@ -0,0 +1 @@
+[ 907, 9.07, "907", 9.07, true, 15706, 621173594, null ]
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/results/external-library/python_open_type_validation/type_validation.4.adm b/asterixdb/asterix-app/src/test/resources/runtimets/results/external-library/python_open_type_validation/type_validation.4.adm
new file mode 100644
index 0000000..53fd925
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/results/external-library/python_open_type_validation/type_validation.4.adm
@@ -0,0 +1 @@
+[ 907, 9.07, "907", 9.07, true, 15706, 621173594, null ]
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/results/external-library/python_open_type_validation/type_validation.5.adm b/asterixdb/asterix-app/src/test/resources/runtimets/results/external-library/python_open_type_validation/type_validation.5.adm
new file mode 100644
index 0000000..ec747fa
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/results/external-library/python_open_type_validation/type_validation.5.adm
@@ -0,0 +1 @@
+null
\ No newline at end of file
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/results/external-library/python_open_type_validation/type_validation.6.adm b/asterixdb/asterix-app/src/test/resources/runtimets/results/external-library/python_open_type_validation/type_validation.6.adm
new file mode 100644
index 0000000..ec747fa
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/results/external-library/python_open_type_validation/type_validation.6.adm
@@ -0,0 +1 @@
+null
\ No newline at end of file
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/results/external-library/python_open_type_validation/type_validation.7.adm b/asterixdb/asterix-app/src/test/resources/runtimets/results/external-library/python_open_type_validation/type_validation.7.adm
new file mode 100644
index 0000000..53fd925
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/results/external-library/python_open_type_validation/type_validation.7.adm
@@ -0,0 +1 @@
+[ 907, 9.07, "907", 9.07, true, 15706, 621173594, null ]
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/results/external-library/python_open_type_validation/type_validation.8.adm b/asterixdb/asterix-app/src/test/resources/runtimets/results/external-library/python_open_type_validation/type_validation.8.adm
new file mode 100644
index 0000000..53fd925
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/results/external-library/python_open_type_validation/type_validation.8.adm
@@ -0,0 +1 @@
+[ 907, 9.07, "907", 9.07, true, 15706, 621173594, null ]
diff --git a/asterixdb/asterix-external-data/src/main/java/org/apache/asterix/external/library/ExternalScalarPythonFunctionEvaluator.java b/asterixdb/asterix-external-data/src/main/java/org/apache/asterix/external/library/ExternalScalarPythonFunctionEvaluator.java
index e664f47..eb87399 100644
--- a/asterixdb/asterix-external-data/src/main/java/org/apache/asterix/external/library/ExternalScalarPythonFunctionEvaluator.java
+++ b/asterixdb/asterix-external-data/src/main/java/org/apache/asterix/external/library/ExternalScalarPythonFunctionEvaluator.java
@@ -19,6 +19,7 @@
 
 package org.apache.asterix.external.library;
 
+import static org.apache.asterix.om.types.EnumDeserializer.ATYPETAGDESERIALIZER;
 import static org.msgpack.core.MessagePack.Code.FIXARRAY_PREFIX;
 
 import java.io.DataOutput;
@@ -88,17 +89,31 @@
     @Override
     public void evaluate(IFrameTupleReference tuple, IPointable result) throws HyracksDataException {
         argHolder.clear();
+        boolean nullCall = finfo.getNullCall();
+        boolean hasNullArg = false;
         for (int i = 0, ln = argEvals.length; i < ln; i++) {
             argEvals[i].evaluate(tuple, argValues[i]);
-            if (!finfo.getNullCall() && PointableHelper.checkAndSetMissingOrNull(result, argValues[i])) {
-                return;
+            if (!nullCall) {
+                byte[] argBytes = argValues[i].getByteArray();
+                int argStart = argValues[i].getStartOffset();
+                ATypeTag argType = ATYPETAGDESERIALIZER.deserialize(argBytes[argStart]);
+                if (argType == ATypeTag.MISSING) {
+                    PointableHelper.setMissing(result);
+                    return;
+                } else if (argType == ATypeTag.NULL) {
+                    hasNullArg = true;
+                }
             }
             try {
-                PythonLibraryEvaluator.setArgument(argTypes[i], argValues[i], argHolder, finfo.getNullCall());
+                PythonLibraryEvaluator.setArgument(argTypes[i], argValues[i], argHolder, nullCall);
             } catch (IOException e) {
                 throw new HyracksDataException("Error evaluating Python UDF", e);
             }
         }
+        if (!nullCall && hasNullArg) {
+            PointableHelper.setNull(result);
+            return;
+        }
         try {
             ByteBuffer res = libraryEvaluator.callPython(fnId, argHolder, argTypes.length);
             resultBuffer.reset();