[JAVA-5203] Support stored nulls for non-primitive fields in Java records

bson-record-codec/src/main/org/bson/codecs/record/RecordCodec.java

@@ -62,6 +62,7 @@ private static final class ComponentModel {
         private final Codec<?> codec;
         private final int index;
         private final String fieldName;
+        private final boolean isNullable;
 
         private ComponentModel(final List<Type> typeParameters, final RecordComponent component, final CodecRegistry codecRegistry,
                 final int index) {
@@ -70,6 +71,7 @@ private ComponentModel(final List<Type> typeParameters, final RecordComponent co
             this.codec = computeCodec(typeParameters, component, codecRegistry);
             this.index = index;
             this.fieldName = computeFieldName(component);
+            this.isNullable = !component.getType().isPrimitive();
         }
 
         String getComponentName() {
@@ -275,6 +277,8 @@ public T decode(final BsonReader reader, final DecoderContext decoderContext) {
                 if (LOGGER.isTraceEnabled()) {
                     LOGGER.trace(format("Found property not present in the ClassModel: %s", fieldName));
                 }
+            } else if (reader.getCurrentBsonType() == BsonType.NULL && componentModel.isNullable) {
+                reader.readNull();
             } else {
                 constructorArguments[componentModel.index] = decoderContext.decodeWithChildContext(componentModel.codec, reader);
             }

bson-record-codec/src/test/unit/org/bson/codecs/record/RecordCodecTest.java

@@ -22,6 +22,7 @@
 import org.bson.BsonDocumentWriter;
 import org.bson.BsonDouble;
 import org.bson.BsonInt32;
+import org.bson.BsonNull;
 import org.bson.BsonObjectId;
 import org.bson.BsonString;
 import org.bson.codecs.DecoderContext;
@@ -49,6 +50,7 @@
 import org.bson.codecs.record.samples.TestRecordWithMapOfRecords;
 import org.bson.codecs.record.samples.TestRecordWithNestedParameterized;
 import org.bson.codecs.record.samples.TestRecordWithNestedParameterizedRecord;
+import org.bson.codecs.record.samples.TestRecordWithNullableField;
 import org.bson.codecs.record.samples.TestRecordWithParameterizedRecord;
 import org.bson.codecs.record.samples.TestRecordWithPojoAnnotations;
 import org.bson.codecs.record.samples.TestSelfReferentialHolderRecord;
@@ -325,6 +327,22 @@ public void testRecordWithNulls() {
         assertEquals(testRecord, decoded);
     }
 
+    @Test
+    public void testRecordWithStoredNulls() {
+        var codec = createRecordCodec(TestRecordWithNullableField.class, Bson.DEFAULT_CODEC_REGISTRY);
+        var identifier = new ObjectId();
+        var testRecord = new TestRecordWithNullableField(identifier, null);
+
+        var document = new BsonDocument("_id", new BsonObjectId(identifier))
+                .append("name", new BsonNull());
+
+        // when
+        var decoded = codec.decode(new BsonDocumentReader(document), DecoderContext.builder().build());
+
+        // then
+        assertEquals(testRecord, decoded);
+    }
+
     @Test
     public void testRecordWithExtraData() {
         var codec = createRecordCodec(TestRecordWithDeprecatedAnnotations.class, Bson.DEFAULT_CODEC_REGISTRY);

bson-record-codec/src/test/unit/org/bson/codecs/record/samples/TestRecordWithNullableField.java

@@ -0,0 +1,23 @@
+/*
+ * Copyright 2008-present MongoDB, Inc.
+ *
+ * Licensed 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.bson.codecs.record.samples;
+
+import org.bson.codecs.pojo.annotations.BsonId;
+import org.bson.types.ObjectId;
+
+public record TestRecordWithNullableField(@BsonId ObjectId id, String name) {
+}