Example UDF and its unit test to repro issue: https://github.com/link…

transportable-udfs-examples/transportable-udfs-example-udfs/src/main/java/com/linkedin/transport/examples/StructElementIncrementByOneFunction.java

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+/**
+ * Copyright 2023 LinkedIn Corporation. All rights reserved.
+ * Licensed under the BSD-2 Clause license.
+ * See LICENSE in the project root for license information.
+ */
+package com.linkedin.transport.examples;
+
+import com.google.common.collect.ImmutableList;
+import com.linkedin.transport.api.data.StdInteger;
+import com.linkedin.transport.api.data.StdStruct;
+import com.linkedin.transport.api.udf.StdUDF1;
+import com.linkedin.transport.api.udf.TopLevelStdUDF;
+import java.util.List;
+
+
+public class StructElementIncrementByOneFunction extends StdUDF1<StdStruct, StdStruct> implements TopLevelStdUDF {
+
+  @Override
+  public List<String> getInputParameterSignatures() {
+    return ImmutableList.of(
+        "row(integer, integer)"
+    );
+  }
+
+  @Override
+  public String getOutputParameterSignature() {
+    return "row(integer, integer)";
+  }
+
+  @Override
+  public StdStruct eval(StdStruct myStruct) {
+    int currVal = ((StdInteger) myStruct.getField(0)).get();
+    myStruct.setField(0, getStdFactory().createInteger(currVal + 1));
+    return myStruct;
+  }
+
+  @Override
+  public String getFunctionName() {
+    return "struct_element_increment_by_one";
+  }
+
+  @Override
+  public String getFunctionDescription() {
+    return "increment first element by one";
+  }
+}

transportable-udfs-examples/transportable-udfs-example-udfs/src/test/java/com/linkedin/transport/examples/TestStructElementIncrementByOneFunction.java

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+/**
+ * Copyright 2023 LinkedIn Corporation. All rights reserved.
+ * Licensed under the BSD-2 Clause license.
+ * See LICENSE in the project root for license information.
+ */
+package com.linkedin.transport.examples;
+
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableMap;
+import com.linkedin.transport.api.udf.StdUDF;
+import com.linkedin.transport.api.udf.TopLevelStdUDF;
+import com.linkedin.transport.test.AbstractStdUDFTest;
+import com.linkedin.transport.test.spi.StdTester;
+import java.util.List;
+import java.util.Map;
+import org.testng.annotations.Test;
+
+
+public class TestStructElementIncrementByOneFunction extends AbstractStdUDFTest {
+
+  @Override
+  protected Map<Class<? extends TopLevelStdUDF>, List<Class<? extends StdUDF>>> getTopLevelStdUDFClassesAndImplementations() {
+    return ImmutableMap.of(
+        StructElementIncrementByOneFunction.class, ImmutableList.of(StructElementIncrementByOneFunction.class));
+  }
+
+  @Test
+  public void testStructElementIncrementByOneFunction() {
+    StdTester tester = getTester();
+    tester.check(functionCall("struct_element_increment_by_one", row(1, 3)), row(2, 3), "row(integer,integer)");
+    tester.check(functionCall("struct_element_increment_by_one", row(-2, 3)), row(-1, 3), "row(integer,integer)");
+  }
+}