[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 = checkFieldIsNullable(component);
         }
 
         String getComponentName() {
@@ -156,6 +158,14 @@ private static String computeFieldName(final RecordComponent component) {
             return component.getName();
         }
 
+        private static boolean checkFieldIsNullable(final RecordComponent component) {
+            try {
+                return component.getDeclaringRecord().getDeclaredField(component.getName()).isAnnotationPresent(Nullable.class);
+            } catch (NoSuchFieldException e) {
+                throw new AssertionError(format("Unexpectedly missing the declared field for recordComponent %s", component), e);
+            }
+        }
+
         private static <T extends Annotation> boolean isAnnotationPresentOnField(final RecordComponent component,
                 final Class<T> annotation) {
             try {
@@ -275,6 +285,8 @@ 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.TestRecordWithNullableAnnotation;
 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(TestRecordWithNullableAnnotation.class, Bson.DEFAULT_CODEC_REGISTRY);
+        var identifier = new ObjectId();
+        var testRecord = new TestRecordWithNullableAnnotation(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/TestRecordWithNullableAnnotation.java

@@ -0,0 +1,9 @@
+package org.bson.codecs.record.samples;
+
+import org.bson.codecs.pojo.annotations.BsonId;
+import org.bson.types.ObjectId;
+
+import javax.annotation.Nullable;
+
+public record TestRecordWithNullableAnnotation (@BsonId ObjectId id, @Nullable String name) {
+}