fix: obj -> fr -> obj preserves boolean nullability

Author: eduardoramirez

hollow/src/main/java/com/netflix/hollow/core/write/objectmapper/HollowObjectTypeMapper.java

@@ -589,7 +589,9 @@ public void copy(Object obj, HollowObjectWriteRecord rec, FlatRecordWriter flatR
         public void copy(Object pojo, GenericHollowObject rec) {
             switch (fieldType) {
                 case BOOLEAN:
-                    unsafe.putBoolean(pojo, fieldOffset, rec.getBoolean(fieldName));
+                    if (!rec.isNull(fieldName)) {
+                        unsafe.putBoolean(pojo, fieldOffset, rec.getBoolean(fieldName));
+                    }
                     break;
                 case INT:
                     int intValue = rec.getInt(fieldName);
@@ -833,9 +835,9 @@ private Object parseBoxedWrapper(FlatRecordTraversalObjectNode record) {
         private void copy(Object obj, FlatRecordTraversalObjectNode node) {
             switch (fieldType) {
                 case BOOLEAN: {
-                    Boolean value = node.getFieldValueBooleanBoxed(fieldName);
-                    if (value != null) {
-                        unsafe.putBoolean(obj, fieldOffset, value == Boolean.TRUE);
+                    if (!node.isFieldNull(fieldName)) {
+                        boolean value = node.getFieldValueBoolean(fieldName);
+                        unsafe.putBoolean(obj, fieldOffset, value);
                     }
                     break;
                 }
@@ -901,8 +903,8 @@ private void copy(Object obj, FlatRecordTraversalObjectNode node) {
                     break;
                 }
                 case INLINED_BOOLEAN: {
-                    Boolean value = node.getFieldValueBooleanBoxed(fieldName);
-                    if (value != null) {
+                    if (!node.isFieldNull(fieldName)) {
+                        boolean value = node.getFieldValueBoolean(fieldName);
                         unsafe.putObject(obj, fieldOffset, value);
                     }
                     break;

hollow/src/test/java/com/netflix/hollow/core/write/objectmapper/HollowObjectMapperFlatRecordParserTest.java

@@ -52,6 +52,31 @@ public void testSpecialWrapperTypes() {
     Assert.assertEquals(wrapperTypesTest.complexEnum.anotherValue, result.complexEnum.anotherValue);
   }
 
+  @Test
+  public void roundTripPreservesNullability() {
+    TypeWithAllSimpleTypes obj = new TypeWithAllSimpleTypes();
+    // set PK
+    obj.boxedIntegerField = 1;
+    obj.stringField = "hello";
+    // all inlined values are null
+
+    flatRecordWriter.reset();
+    mapper.writeFlat(obj, flatRecordWriter);
+    FlatRecord fr = flatRecordWriter.generateFlatRecord();
+
+    TypeWithAllSimpleTypes result = mapper.readFlat(fr);
+    Assert.assertEquals(obj, result);
+
+    // round trip the record: obj -> flatRecord -> obj -> flatRecord -> obj
+    flatRecordWriter.reset();
+    TypeWithAllSimpleTypes roundTrippedObj = mapper.readFlat(fr);
+    mapper.writeFlat(roundTrippedObj, flatRecordWriter);
+    FlatRecord roundTrippedFr = flatRecordWriter.generateFlatRecord();
+
+    TypeWithAllSimpleTypes roundTrippedResult = mapper.readFlat(roundTrippedFr);
+    Assert.assertEquals(obj, roundTrippedResult);
+  }
+
   @Test
   public void testSimpleTypes() {
     TypeWithAllSimpleTypes typeWithAllSimpleTypes = new TypeWithAllSimpleTypes();