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 d3eb0c2..2c5a07d 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
@@ -115,6 +115,13 @@
         if (op.getOperatorTag() != LogicalOperatorTag.ASSIGN) {
             return false;
         }
-        return op.acceptExpressionTransform(expr -> rewriteFunctionArgs(op, expr, context));
+        if (context.checkIfInDontApplySet(this, op)) {
+            return false;
+        }
+        boolean applied = op.acceptExpressionTransform(expr -> rewriteFunctionArgs(op, expr, context));
+        if (applied) {
+            context.addToDontApplySet(this, op);
+        }
+        return applied;
     }
 }
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/type_name/type_name.0.ddl.sqlpp b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/type_name/type_name.0.ddl.sqlpp
new file mode 100644
index 0000000..76cc70d
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/type_name/type_name.0.ddl.sqlpp
@@ -0,0 +1,20 @@
+/*
+ * 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 externallibtest if exists;
+CREATE DATAVERSE  externallibtest;
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/type_name/type_name.1.lib.sqlpp b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/type_name/type_name.1.lib.sqlpp
new file mode 100644
index 0000000..b2bf929
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/type_name/type_name.1.lib.sqlpp
@@ -0,0 +1,20 @@
+/*
+ * 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.
+ */
+
+install externallibtest testlib java admin admin target/data/externallib/asterix-external-data-testlib.zip
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/type_name/type_name.2.ddl.sqlpp b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/type_name/type_name.2.ddl.sqlpp
new file mode 100644
index 0000000..c7d6768
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/type_name/type_name.2.ddl.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;
+
+create function typeName(v) returns string
+  as "org.apache.asterix.external.library.TypeNameFactory" at testlib;
+
+create function typeNameNullCall(v) returns string
+  as "org.apache.asterix.external.library.TypeNameFactory" at testlib with {"null-call": true};
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/type_name/type_name.3.query.sqlpp b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/type_name/type_name.3.query.sqlpp
new file mode 100644
index 0000000..2542d55
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/type_name/type_name.3.query.sqlpp
@@ -0,0 +1,28 @@
+/*
+ * 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;
+
+{
+  "missing": typeName(missing) is missing,
+  "missing_nullcall": typeNameNullCall(missing),
+  "null": typeName(null) is null,
+  "null_nullcall": typeNameNullCall(null),
+  "boolean": typeName(true),
+  "string": typeName("x")
+}
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/type_name/type_name.4.ddl.sqlpp b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/type_name/type_name.4.ddl.sqlpp
new file mode 100644
index 0000000..2b27030
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/queries_sqlpp/external-library/type_name/type_name.4.ddl.sqlpp
@@ -0,0 +1,20 @@
+/*
+ * 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 externallibtest;
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/results/external-library/type_name/type_name.3.adm b/asterixdb/asterix-app/src/test/resources/runtimets/results/external-library/type_name/type_name.3.adm
new file mode 100644
index 0000000..a72c46c
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/results/external-library/type_name/type_name.3.adm
@@ -0,0 +1 @@
+{ "missing": true, "missing_nullcall": "missing", "null": true, "null_nullcall": "null", "boolean": "boolean", "string": "string" }
\ No newline at end of file
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/testsuite_it_sqlpp.xml b/asterixdb/asterix-app/src/test/resources/runtimets/testsuite_it_sqlpp.xml
index 28cbabb..6c67216 100644
--- a/asterixdb/asterix-app/src/test/resources/runtimets/testsuite_it_sqlpp.xml
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/testsuite_it_sqlpp.xml
@@ -42,6 +42,11 @@
       </compilation-unit>
     </test-case>
     <test-case FilePath="external-library">
+      <compilation-unit name="type_name">
+        <output-dir compare="Text">type_name</output-dir>
+      </compilation-unit>
+    </test-case>
+    <test-case FilePath="external-library">
       <compilation-unit name="type_validation">
         <output-dir compare="Text">type_validation</output-dir>
       </compilation-unit>
diff --git a/asterixdb/asterix-external-data/src/main/java/org/apache/asterix/external/library/ExternalScalarJavaFunctionEvaluator.java b/asterixdb/asterix-external-data/src/main/java/org/apache/asterix/external/library/ExternalScalarJavaFunctionEvaluator.java
index 33b0369..35d55f7 100755
--- a/asterixdb/asterix-external-data/src/main/java/org/apache/asterix/external/library/ExternalScalarJavaFunctionEvaluator.java
+++ b/asterixdb/asterix-external-data/src/main/java/org/apache/asterix/external/library/ExternalScalarJavaFunctionEvaluator.java
@@ -19,7 +19,7 @@
 
 package org.apache.asterix.external.library;
 
-import java.io.IOException;
+import static org.apache.asterix.om.types.EnumDeserializer.ATYPETAGDESERIALIZER;
 
 import org.apache.asterix.common.exceptions.ErrorCode;
 import org.apache.asterix.common.exceptions.RuntimeDataException;
@@ -27,7 +27,9 @@
 import org.apache.asterix.external.api.IExternalScalarFunction;
 import org.apache.asterix.external.api.IFunctionFactory;
 import org.apache.asterix.om.functions.IExternalFunctionInfo;
+import org.apache.asterix.om.types.ATypeTag;
 import org.apache.asterix.om.types.IAType;
+import org.apache.asterix.runtime.evaluators.functions.PointableHelper;
 import org.apache.hyracks.algebricks.runtime.base.IEvaluatorContext;
 import org.apache.hyracks.algebricks.runtime.base.IScalarEvaluatorFactory;
 import org.apache.hyracks.api.exceptions.HyracksDataException;
@@ -71,23 +73,36 @@
     @Override
     public void evaluate(IFrameTupleReference tuple, IPointable result) throws HyracksDataException {
         try {
-            setArguments(tuple);
-            resultBuffer.reset();
-            externalFunctionInstance.evaluate(functionHelper);
-            if (!functionHelper.isValidResult()) {
-                throw new RuntimeDataException(ErrorCode.EXTERNAL_UDF_RESULT_TYPE_ERROR);
+            boolean nullCall = finfo.getNullCall();
+            boolean hasNullArg = false;
+            for (int i = 0; i < argEvals.length; i++) {
+                argEvals[i].evaluate(tuple, inputVal);
+                if (!nullCall) {
+                    byte[] inputValBytes = inputVal.getByteArray();
+                    int inputValStartOffset = inputVal.getStartOffset();
+                    ATypeTag typeTag = ATYPETAGDESERIALIZER.deserialize(inputValBytes[inputValStartOffset]);
+                    if (typeTag == ATypeTag.MISSING) {
+                        PointableHelper.setMissing(result);
+                        return;
+                    } else if (typeTag == ATypeTag.NULL) {
+                        hasNullArg = true;
+                    }
+                }
+                functionHelper.setArgument(i, inputVal);
             }
-            result.set(resultBuffer.getByteArray(), resultBuffer.getStartOffset(), resultBuffer.getLength());
-            functionHelper.reset();
+            if (!nullCall && hasNullArg) {
+                PointableHelper.setNull(result);
+            } else {
+                resultBuffer.reset();
+                externalFunctionInstance.evaluate(functionHelper);
+                if (!functionHelper.isValidResult()) {
+                    throw new RuntimeDataException(ErrorCode.EXTERNAL_UDF_RESULT_TYPE_ERROR);
+                }
+                result.set(resultBuffer.getByteArray(), resultBuffer.getStartOffset(), resultBuffer.getLength());
+                functionHelper.reset();
+            }
         } catch (Exception e) {
             throw HyracksDataException.create(e);
         }
     }
-
-    public void setArguments(IFrameTupleReference tuple) throws IOException {
-        for (int i = 0; i < argEvals.length; i++) {
-            argEvals[i].evaluate(tuple, inputVal);
-            functionHelper.setArgument(i, inputVal);
-        }
-    }
 }
diff --git a/asterixdb/asterix-external-data/src/test/java/org/apache/asterix/external/library/TypeNameFactory.java b/asterixdb/asterix-external-data/src/test/java/org/apache/asterix/external/library/TypeNameFactory.java
new file mode 100644
index 0000000..335c383
--- /dev/null
+++ b/asterixdb/asterix-external-data/src/test/java/org/apache/asterix/external/library/TypeNameFactory.java
@@ -0,0 +1,30 @@
+/*
+ * 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.
+ */
+
+package org.apache.asterix.external.library;
+
+import org.apache.asterix.external.api.IExternalScalarFunction;
+import org.apache.asterix.external.api.IFunctionFactory;
+
+public class TypeNameFactory implements IFunctionFactory {
+    @Override
+    public IExternalScalarFunction getExternalFunction() {
+        return new TypeNameFunction();
+    }
+}
diff --git a/asterixdb/asterix-external-data/src/test/java/org/apache/asterix/external/library/TypeNameFunction.java b/asterixdb/asterix-external-data/src/test/java/org/apache/asterix/external/library/TypeNameFunction.java
new file mode 100644
index 0000000..1f03fcc
--- /dev/null
+++ b/asterixdb/asterix-external-data/src/test/java/org/apache/asterix/external/library/TypeNameFunction.java
@@ -0,0 +1,46 @@
+/*
+ * 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.
+ */
+
+package org.apache.asterix.external.library;
+
+import org.apache.asterix.external.api.IExternalScalarFunction;
+import org.apache.asterix.external.api.IFunctionHelper;
+import org.apache.asterix.external.library.java.base.JString;
+
+public class TypeNameFunction implements IExternalScalarFunction {
+
+    private JString result;
+
+    @Override
+    public void deinitialize() {
+        // nothing to do here
+    }
+
+    @Override
+    public void evaluate(IFunctionHelper functionHelper) throws Exception {
+        String arg0TypeName = functionHelper.getArgument(0).getIAType().getTypeName();
+        result.setValue(arg0TypeName);
+        functionHelper.setResult(result);
+    }
+
+    @Override
+    public void initialize(IFunctionHelper functionHelper) {
+        result = (JString) functionHelper.getResultObject();
+    }
+}
diff --git a/asterixdb/asterix-metadata/src/main/java/org/apache/asterix/metadata/functions/ExternalFunctionCompilerUtil.java b/asterixdb/asterix-metadata/src/main/java/org/apache/asterix/metadata/functions/ExternalFunctionCompilerUtil.java
index 6751171..5fd96a6 100644
--- a/asterixdb/asterix-metadata/src/main/java/org/apache/asterix/metadata/functions/ExternalFunctionCompilerUtil.java
+++ b/asterixdb/asterix-metadata/src/main/java/org/apache/asterix/metadata/functions/ExternalFunctionCompilerUtil.java
@@ -69,7 +69,7 @@
 
         IAType returnType = getType(function.getReturnType(), metadataProvider);
 
-        IResultTypeComputer typeComputer = new ExternalTypeComputer(returnType, paramTypes);
+        IResultTypeComputer typeComputer = new ExternalTypeComputer(returnType, paramTypes, function.getNullCall());
 
         ExternalFunctionLanguage lang = getExternalFunctionLanguage(function.getLanguage());
 
diff --git a/asterixdb/asterix-metadata/src/main/java/org/apache/asterix/metadata/functions/ExternalTypeComputer.java b/asterixdb/asterix-metadata/src/main/java/org/apache/asterix/metadata/functions/ExternalTypeComputer.java
index 4a000a3..99d8ea2 100644
--- a/asterixdb/asterix-metadata/src/main/java/org/apache/asterix/metadata/functions/ExternalTypeComputer.java
+++ b/asterixdb/asterix-metadata/src/main/java/org/apache/asterix/metadata/functions/ExternalTypeComputer.java
@@ -33,8 +33,9 @@
 
 public class ExternalTypeComputer extends AbstractResultTypeComputer {
 
-    private IAType resultType;
-    private List<IAType> paramPrimeTypes;
+    private final IAType resultType;
+    private final List<IAType> paramPrimeTypes;
+    private final boolean nullCall;
 
     @Override
     protected void checkArgType(FunctionIdentifier funcId, int argIndex, IAType type, SourceLocation sourceLoc)
@@ -47,14 +48,20 @@
         }
     }
 
-    public ExternalTypeComputer(IAType resultPrimeType, List<IAType> paramPrimeTypes) {
+    public ExternalTypeComputer(IAType resultPrimeType, List<IAType> paramPrimeTypes, boolean nullCall) {
         this.resultType = resultPrimeType.getTypeTag() == ATypeTag.ANY ? resultPrimeType
                 : AUnionType.createUnknownableType(resultPrimeType);
         this.paramPrimeTypes = paramPrimeTypes;
+        this.nullCall = nullCall;
     }
 
     @Override
     protected IAType getResultType(ILogicalExpression expr, IAType... strippedInputTypes) {
         return resultType;
     }
+
+    @Override
+    protected boolean propagateNullAndMissing() {
+        return !nullCall;
+    }
 }