Update Nullable constraints.

See: #4874

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/SessionAwareMethodInterceptor.java

@@ -165,6 +165,7 @@ public class SessionAwareMethodInterceptor<D, C> implements MethodInterceptor {
 		 * @param targetClass
 		 * @return
 		 */
+		@SuppressWarnings("NullAway")
 		Optional<Method> lookup(Method method, Class<?> targetClass, Class<? extends ClientSession> sessionType) {
 
 			return cache.computeIfAbsent(new MethodClassKey(method, targetClass),

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/DefaultReactiveBulkOperations.java

@@ -133,7 +133,7 @@ class DefaultReactiveBulkOperations extends BulkOperationsSupport implements Rea
 	}
 
 	@Override
-	@Contract("_, _, _ -> this")
+	@Contract("_, _ -> this")
 	public ReactiveBulkOperations updateOne(Query query, UpdateDefinition update) {
 
 		Assert.notNull(query, "Query must not be null");

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/MongoTemplate.java

@@ -1986,6 +1986,7 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 	 * @deprecated since 3.4 in favor of {@link #aggregate(TypedAggregation, Class)}.
 	 */
 	@Deprecated
+	@SuppressWarnings("NullAway")
 	public <T> List<T> mapReduce(Query query, Class<?> domainType, String inputCollectionName, String mapFunction,
 			String reduceFunction, @Nullable MapReduceOptions mapReduceOptions, Class<T> resultType) {
 

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/AddFieldsOperation.java

@@ -84,7 +84,7 @@ public class AddFieldsOperation extends DocumentEnhancingOperation {
 	 * @param value the value to assign.
 	 * @return new instance of {@link AddFieldsOperation}.
 	 */
-	@Contract("_ -> new")
+	@Contract("_, _ -> new")
 	public AddFieldsOperation addField(Object field, Object value) {
 
 		LinkedHashMap<Object, Object> target = new LinkedHashMap<>(getValueMap());

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/DateOperators.java

@@ -2717,7 +2717,7 @@ public class DateOperators {
 		 *
 		 * @return new instance of {@link DateToParts}.
 		 */
-		@Contract("_ -> new")
+		@Contract("-> new")
 		public DateToParts iso8601() {
 			return new DateToParts(append("iso8601", true));
 		}

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/Fields.java

@@ -151,7 +151,7 @@ public final class Fields implements Iterable<Field> {
 		return and(new AggregationField(name));
 	}
 
-	@Contract("_ -> new")
+	@Contract("_, _ -> new")
 	public Fields and(String name, String target) {
 		return and(new AggregationField(name, target));
 	}

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/SetWindowFieldsOperation.java

@@ -518,7 +518,7 @@ public class SetWindowFieldsOperation
 			return from(UNBOUNDED);
 		}
 
-		@Contract("-> this")
+		@Contract("_ -> this")
 		public DocumentWindowBuilder to(String upper) {
 
 			this.upper = upper;

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/convert/GeoConverters.java

@@ -65,7 +65,7 @@ import com.mongodb.Function;
 @SuppressWarnings("ConstantConditions")
 abstract class GeoConverters {
 
-	private final static Map<String, Function<Document, GeoJson<?>>> converters;
+	private final static Map<String, Function<Document, @Nullable GeoJson<?>>> converters;
 
 	static {
 
@@ -127,15 +127,15 @@ abstract class GeoConverters {
 	 * @since 1.5
 	 */
 	@ReadingConverter
-	enum DocumentToPointConverter implements Converter<Document, Point> {
+	enum DocumentToPointConverter implements Converter<Document, @Nullable Point> {
 
 		INSTANCE;
 
 		@Override
-		@Contract("null -> null; !null -> !null")
-		public @Nullable Point convert(@Nullable Document source) {
+		@SuppressWarnings("NullAway")
+		public Point convert(Document source) {
 
-			if (source == null) {
+			if(ObjectUtils.isEmpty(source)) {
 				return null;
 			}
 
@@ -155,6 +155,7 @@ abstract class GeoConverters {
 	 * @author Thomas Darimont
 	 * @since 1.5
 	 */
+	@SuppressWarnings("NullAway")
 	enum PointToDocumentConverter implements Converter<Point, Document> {
 
 		INSTANCE;
@@ -173,6 +174,7 @@ abstract class GeoConverters {
 	 * @since 1.5
 	 */
 	@WritingConverter
+	@SuppressWarnings("NullAway")
 	enum BoxToDocumentConverter implements Converter<Box, Document> {
 
 		INSTANCE;
@@ -199,21 +201,25 @@ abstract class GeoConverters {
 	 * @since 1.5
 	 */
 	@ReadingConverter
-	enum DocumentToBoxConverter implements Converter<Document, Box> {
+	enum DocumentToBoxConverter implements Converter<Document, @Nullable Box> {
 
 		INSTANCE;
 
 		@Override
-		@Contract("null -> null; !null -> !null")
 		@SuppressWarnings("NullAway")
-		public @Nullable Box convert(@Nullable Document source) {
+		public Box convert(Document source) {
 
-			if (source == null) {
+			if(ObjectUtils.isEmpty(source)) {
 				return null;
 			}
 
-			Point first = DocumentToPointConverter.INSTANCE.convert((Document) source.get("first"));
-			Point second = DocumentToPointConverter.INSTANCE.convert((Document) source.get("second"));
+			Document firstDoc = (Document) source.get("first");
+			Document secondDoc = (Document) source.get("second");
+
+			Assert.notNull(firstDoc, "first must not be null");
+			Assert.notNull(secondDoc, "second must not be null");
+			Point first = DocumentToPointConverter.INSTANCE.convert(firstDoc);
+			Point second = DocumentToPointConverter.INSTANCE.convert(secondDoc);
 
 			return new Box(first, second);
 		}
@@ -225,6 +231,7 @@ abstract class GeoConverters {
 	 * @author Thomas Darimont
 	 * @since 1.5
 	 */
+	@SuppressWarnings("NullAway")
 	enum CircleToDocumentConverter implements Converter<Circle, Document> {
 
 		INSTANCE;
@@ -252,15 +259,15 @@ abstract class GeoConverters {
 	 * @since 1.5
 	 */
 	@ReadingConverter
-	enum DocumentToCircleConverter implements Converter<Document, Circle> {
+	enum DocumentToCircleConverter implements Converter<Document, @Nullable Circle> {
 
 		INSTANCE;
 
 		@Override
-		@Contract("null -> null; !null -> !null")
-		public @Nullable Circle convert(@Nullable Document source) {
+		@SuppressWarnings("NullAway")
+		public Circle convert(Document source) {
 
-			if (source == null) {
+			if(ObjectUtils.isEmpty(source)) {
 				return null;
 			}
 
@@ -290,6 +297,7 @@ abstract class GeoConverters {
 	 * @author Thomas Darimont
 	 * @since 1.5
 	 */
+	@SuppressWarnings("NullAway")
 	enum SphereToDocumentConverter implements Converter<Sphere, Document> {
 
 		INSTANCE;
@@ -317,15 +325,15 @@ abstract class GeoConverters {
 	 * @since 1.5
 	 */
 	@ReadingConverter
-	enum DocumentToSphereConverter implements Converter<Document, Sphere> {
+	enum DocumentToSphereConverter implements Converter<Document, @Nullable Sphere> {
 
 		INSTANCE;
 
 		@Override
-		@Contract("null -> null; !null -> !null")
-		public @Nullable Sphere convert(@Nullable Document source) {
+		@SuppressWarnings("NullAway")
+		public Sphere convert(Document source) {
 
-			if (source == null) {
+			if(ObjectUtils.isEmpty(source)) {
 				return null;
 			}
 
@@ -355,6 +363,7 @@ abstract class GeoConverters {
 	 * @author Thomas Darimont
 	 * @since 1.5
 	 */
+	@SuppressWarnings("NullAway")
 	enum PolygonToDocumentConverter implements Converter<Polygon, Document> {
 
 		INSTANCE;
@@ -387,16 +396,15 @@ abstract class GeoConverters {
 	 * @since 1.5
 	 */
 	@ReadingConverter
-	enum DocumentToPolygonConverter implements Converter<Document, Polygon> {
+	enum DocumentToPolygonConverter implements Converter<Document, @Nullable Polygon> {
 
 		INSTANCE;
 
 		@Override
-		@SuppressWarnings({ "unchecked" })
-		@Contract("null -> null; !null -> !null")
-		public @Nullable Polygon convert(@Nullable Document source) {
+		@SuppressWarnings({ "unchecked", "NullAway" })
+		public Polygon convert(Document source) {
 
-			if (source == null) {
+			if(ObjectUtils.isEmpty(source)) {
 				return null;
 			}
 
@@ -420,6 +428,7 @@ abstract class GeoConverters {
 	 * @author Thomas Darimont
 	 * @since 1.5
 	 */
+	@SuppressWarnings("NullAway")
 	enum GeoCommandToDocumentConverter implements Converter<GeoCommand, Document> {
 
 		INSTANCE;
@@ -473,6 +482,7 @@ abstract class GeoConverters {
 	 * @author Christoph Strobl
 	 * @since 1.7
 	 */
+	@SuppressWarnings("NullAway")
 	enum GeoJsonToDocumentConverter implements Converter<GeoJson<?>, Document> {
 
 		INSTANCE;
@@ -561,16 +571,15 @@ abstract class GeoConverters {
 	 * @author Christoph Strobl
 	 * @since 1.7
 	 */
-	enum DocumentToGeoJsonPointConverter implements Converter<Document, GeoJsonPoint> {
+	enum DocumentToGeoJsonPointConverter implements Converter<Document, @Nullable GeoJsonPoint> {
 
 		INSTANCE;
 
 		@Override
-		@SuppressWarnings("unchecked")
-		@Contract("null -> null; !null -> !null")
-		public @Nullable GeoJsonPoint convert(@Nullable Document source) {
+		@SuppressWarnings({"unchecked", "NullAway"})
+		public GeoJsonPoint convert(Document source) {
 
-			if (source == null) {
+			if(ObjectUtils.isEmpty(source)) {
 				return null;
 			}
 
@@ -589,15 +598,15 @@ abstract class GeoConverters {
 	 * @author Christoph Strobl
 	 * @since 1.7
 	 */
-	enum DocumentToGeoJsonPolygonConverter implements Converter<Document, GeoJsonPolygon> {
+	enum DocumentToGeoJsonPolygonConverter implements Converter<Document, @Nullable GeoJsonPolygon> {
 
 		INSTANCE;
 
 		@Override
-		@Contract("null -> null; !null -> !null")
-		public @Nullable GeoJsonPolygon convert(@Nullable Document source) {
+		@SuppressWarnings("NullAway")
+		public GeoJsonPolygon convert(Document source) {
 
-			if (source == null) {
+			if(ObjectUtils.isEmpty(source)) {
 				return null;
 			}
 
@@ -612,15 +621,15 @@ abstract class GeoConverters {
 	 * @author Christoph Strobl
 	 * @since 1.7
 	 */
-	enum DocumentToGeoJsonMultiPolygonConverter implements Converter<Document, GeoJsonMultiPolygon> {
+	enum DocumentToGeoJsonMultiPolygonConverter implements Converter<Document, @Nullable GeoJsonMultiPolygon> {
 
 		INSTANCE;
 
 		@Override
-		@Contract("null -> null; !null -> !null")
-		public @Nullable GeoJsonMultiPolygon convert(@Nullable Document source) {
+		@SuppressWarnings("NullAway")
+		public GeoJsonMultiPolygon convert(Document source) {
 
-			if (source == null) {
+			if(ObjectUtils.isEmpty(source)) {
 				return null;
 			}
 
@@ -643,15 +652,15 @@ abstract class GeoConverters {
 	 * @author Christoph Strobl
 	 * @since 1.7
 	 */
-	enum DocumentToGeoJsonLineStringConverter implements Converter<Document, GeoJsonLineString> {
+	enum DocumentToGeoJsonLineStringConverter implements Converter<Document, @Nullable GeoJsonLineString> {
 
 		INSTANCE;
 
 		@Override
-		@Contract("null -> null; !null -> !null")
-		public @Nullable GeoJsonLineString convert(@Nullable Document source) {
+		@SuppressWarnings("NullAway")
+		public GeoJsonLineString convert(Document source) {
 
-			if (source == null) {
+			if(ObjectUtils.isEmpty(source)) {
 				return null;
 			}
 
@@ -668,15 +677,15 @@ abstract class GeoConverters {
 	 * @author Christoph Strobl
 	 * @since 1.7
 	 */
-	enum DocumentToGeoJsonMultiPointConverter implements Converter<Document, GeoJsonMultiPoint> {
+	enum DocumentToGeoJsonMultiPointConverter implements Converter<Document, @Nullable GeoJsonMultiPoint> {
 
 		INSTANCE;
 
 		@Override
-		@Contract("null -> null; !null -> !null")
-		public @Nullable GeoJsonMultiPoint convert(@Nullable Document source) {
+		@SuppressWarnings("NullAway")
+		public GeoJsonMultiPoint convert(Document source) {
 
-			if (source == null) {
+			if(ObjectUtils.isEmpty(source)) {
 				return null;
 			}
 
@@ -693,15 +702,15 @@ abstract class GeoConverters {
 	 * @author Christoph Strobl
 	 * @since 1.7
 	 */
-	enum DocumentToGeoJsonMultiLineStringConverter implements Converter<Document, GeoJsonMultiLineString> {
+	enum DocumentToGeoJsonMultiLineStringConverter implements Converter<Document, @Nullable GeoJsonMultiLineString> {
 
 		INSTANCE;
 
 		@Override
-		@Contract("null -> null; !null -> !null")
-		public @Nullable GeoJsonMultiLineString convert(@Nullable Document source) {
+		@SuppressWarnings("NullAway")
+		public GeoJsonMultiLineString convert(Document source) {
 
-			if (source == null) {
+			if(ObjectUtils.isEmpty(source)) {
 				return null;
 			}
 
@@ -725,15 +734,15 @@ abstract class GeoConverters {
 	 * @author Christoph Strobl
 	 * @since 1.7
 	 */
-	enum DocumentToGeoJsonGeometryCollectionConverter implements Converter<Document, GeoJsonGeometryCollection> {
+	enum DocumentToGeoJsonGeometryCollectionConverter implements Converter<Document, @Nullable GeoJsonGeometryCollection> {
 
 		INSTANCE;
 
 		@Override
-		@Contract("null -> null; !null -> !null")
-		public @Nullable GeoJsonGeometryCollection convert(@Nullable Document source) {
+		@SuppressWarnings("NullAway")
+		public GeoJsonGeometryCollection convert(Document source) {
 
-			if (source == null) {
+			if(ObjectUtils.isEmpty(source)) {
 				return null;
 			}
 
@@ -808,11 +817,17 @@ abstract class GeoConverters {
 	 * @author Christoph Strobl
 	 */
 	@ReadingConverter
-	enum DocumentToGeoJsonConverter implements Converter<Document, GeoJson<?>> {
+	enum DocumentToGeoJsonConverter implements Converter<Document, @Nullable GeoJson<?>> {
 		INSTANCE;
 
 		@Override
+		@SuppressWarnings("NullAway")
 		public GeoJson<?> convert(Document source) {
+
+			if(ObjectUtils.isEmpty(source)) {
+				return null;
+			}
+
 			return toGenericGeoJson(source);
 		}
 	}

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/convert/MongoConverters.java

@@ -194,10 +194,11 @@ abstract class MongoConverters {
 	 *
 	 * @author Oliver Gierke
 	 */
-	enum StringToObjectIdConverter implements Converter<String, ObjectId> {
+	@SuppressWarnings("NullAway")
+	enum StringToObjectIdConverter implements Converter<String, @Nullable ObjectId> {
 		INSTANCE;
 
-		public @Nullable ObjectId convert(String source) {
+		public ObjectId convert(String source) {
 			return StringUtils.hasText(source) ? new ObjectId(source) : null;
 		}
 	}
@@ -262,10 +263,11 @@ abstract class MongoConverters {
 	}
 
 	@ReadingConverter
-	enum StringToBigDecimalConverter implements Converter<String, BigDecimal> {
+	@SuppressWarnings("NullAway")
+	enum StringToBigDecimalConverter implements Converter<String, @Nullable BigDecimal> {
 		INSTANCE;
 
-		public @Nullable BigDecimal convert(String source) {
+		public BigDecimal convert(String source) {
 			return StringUtils.hasText(source) ? new BigDecimal(source) : null;
 		}
 	}
@@ -292,10 +294,11 @@ abstract class MongoConverters {
 	}
 
 	@ReadingConverter
-	enum StringToBigIntegerConverter implements Converter<String, BigInteger> {
+	@SuppressWarnings("NullAway")
+	enum StringToBigIntegerConverter implements Converter<String, @Nullable BigInteger> {
 		INSTANCE;
 
-		public @Nullable BigInteger convert(String source) {
+		public BigInteger convert(String source) {
 			return StringUtils.hasText(source) ? new BigInteger(source) : null;
 		}
 	}
@@ -439,12 +442,13 @@ abstract class MongoConverters {
 	 * @since 1.9
 	 */
 	@ReadingConverter
-	enum StringToCurrencyConverter implements Converter<String, Currency> {
+	@SuppressWarnings("NullAway")
+	enum StringToCurrencyConverter implements Converter<String, @Nullable Currency> {
 
 		INSTANCE;
 
 		@Override
-		public @Nullable Currency convert(String source) {
+		public Currency convert(String source) {
 			return StringUtils.hasText(source) ? Currency.getInstance(source) : null;
 		}
 	}

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/convert/QueryMapper.java

@@ -1595,7 +1595,8 @@ public class QueryMapper {
 	 *
 	 * @author Oliver Gierke
 	 */
-	protected static class AssociationConverter implements Converter<MongoPersistentProperty, String> {
+	@SuppressWarnings("NullAway")
+	protected static class AssociationConverter implements Converter<MongoPersistentProperty, @Nullable String> {
 
 		private final String name;
 		private final MongoPersistentProperty property;
@@ -1614,7 +1615,7 @@ public class QueryMapper {
 		}
 
 		@Override
-		public @Nullable String convert(MongoPersistentProperty source) {
+		public String convert(MongoPersistentProperty source) {
 
 			if (associationFound) {
 				return null;

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/convert/UpdateMapper.java

@@ -329,6 +329,7 @@ public class UpdateMapper extends QueryMapper {
 		 *
 		 * @author Christoph Strobl
 		 */
+		@SuppressWarnings("NullAway")
 		protected static class UpdateAssociationConverter extends AssociationConverter {
 
 			private final KeyMapper mapper;
@@ -347,7 +348,7 @@ public class UpdateMapper extends QueryMapper {
 			}
 
 			@Override
-			public @Nullable String convert(MongoPersistentProperty source) {
+			public String convert(MongoPersistentProperty source) {
 				return super.convert(source) == null ? null : mapper.mapPropertyName(source);
 			}
 		}

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/index/WildcardIndex.java

@@ -115,7 +115,7 @@ public class WildcardIndex extends Index {
 	 * @throws UnsupportedOperationException not supported for wildcard indexes.
 	 */
 	@Override
-	@Contract("-> fail")
+	@Contract("_ -> fail")
 	public Index expire(long seconds) {
 		throw new UnsupportedOperationException("Wildcard Index does not support 'ttl'");
 	}

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/messaging/TailableCursorRequest.java

@@ -267,7 +267,7 @@ public class TailableCursorRequest<T> implements SubscriptionRequest<Document, T
 		/**
 		 * @return the build {@link ChangeStreamRequest}.
 		 */
-		@Contract("_ -> new")
+		@Contract("-> new")
 		public TailableCursorRequest<T> build() {
 
 			Assert.notNull(listener, "MessageListener must not be null");

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/query/Collation.java

@@ -307,7 +307,7 @@ public class Collation {
 	 *
 	 * @return new {@link Collation}.
 	 */
-	@Contract("_ -> new")
+	@Contract("-> new")
 	public Collation backwardDiacriticSort() {
 		return backwards(true);
 	}

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/query/SerializationUtils.java

@@ -149,6 +149,7 @@ public abstract class SerializationUtils {
 				entry -> String.format("\"%s\" : %s", entry.getKey(), serializeToJsonSafely(entry.getValue())));
 	}
 
+	@SuppressWarnings("NullAway")
 	private static String toString(Collection<?> source) {
 		return iterableToDelimitedString(source, "[ ", " ]", SerializationUtils::serializeToJsonSafely);
 	}

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/schema/IdentifiableJsonSchemaProperty.java

@@ -197,7 +197,7 @@ public class IdentifiableJsonSchemaProperty<T extends JsonSchemaObject> implemen
 		 * @return new instance of {@link StringJsonSchemaProperty}.
 		 * @see StringJsonSchemaObject#generateDescription()
 		 */
-		@Contract("_ -> new")
+		@Contract("-> new")
 		public UntypedJsonSchemaProperty generatedDescription() {
 			return new UntypedJsonSchemaProperty(identifier, jsonSchemaObjectDelegate.generatedDescription());
 		}
@@ -354,7 +354,7 @@ public class IdentifiableJsonSchemaProperty<T extends JsonSchemaObject> implemen
 		 * @return new instance of {@link StringJsonSchemaProperty}.
 		 * @see StringJsonSchemaObject#generateDescription()
 		 */
-		@Contract("_ -> new")
+		@Contract("-> new")
 		public StringJsonSchemaProperty generatedDescription() {
 			return new StringJsonSchemaProperty(identifier, jsonSchemaObjectDelegate.generatedDescription());
 		}
@@ -552,7 +552,7 @@ public class IdentifiableJsonSchemaProperty<T extends JsonSchemaObject> implemen
 		 * @return new instance of {@link ObjectJsonSchemaProperty}.
 		 * @see ObjectJsonSchemaObject#generateDescription()
 		 */
-		@Contract("_ -> new")
+		@Contract("-> new")
 		public ObjectJsonSchemaProperty generatedDescription() {
 			return new ObjectJsonSchemaProperty(identifier, jsonSchemaObjectDelegate.generatedDescription());
 		}

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/schema/TypedJsonSchemaObject.java

@@ -421,7 +421,7 @@ public class TypedJsonSchemaObject extends UntypedJsonSchemaObject {
 		}
 
 		@Override
-		@Contract("_ -> new")
+		@Contract("-> new")
 		public ObjectJsonSchemaObject generatedDescription() {
 			return newInstance(description, true, restrictions);
 		}
@@ -696,7 +696,7 @@ public class TypedJsonSchemaObject extends UntypedJsonSchemaObject {
 		}
 
 		@Override
-		@Contract("_ -> new")
+		@Contract("-> new")
 		public NumericJsonSchemaObject generatedDescription() {
 			return newInstance(description, true, restrictions);
 		}
@@ -1110,7 +1110,7 @@ public class TypedJsonSchemaObject extends UntypedJsonSchemaObject {
 		}
 
 		@Override
-		@Contract("_ -> new")
+		@Contract("-> new")
 		public ArrayJsonSchemaObject generatedDescription() {
 			return newInstance(description, true, restrictions);
 		}
@@ -1242,7 +1242,7 @@ public class TypedJsonSchemaObject extends UntypedJsonSchemaObject {
 		}
 
 		@Override
-		@Contract("_ -> new")
+		@Contract("-> new")
 		public BooleanJsonSchemaObject generatedDescription() {
 			return new BooleanJsonSchemaObject(description, true, restrictions);
 		}

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/util/BsonUtils.java

@@ -797,6 +797,7 @@ public class BsonUtils {
 				entry -> "\"" + entry.getKey() + "\" : " + toJson(entry.getValue()));
 	}
 
+	@SuppressWarnings("NullAway")
 	private static String toString(Collection<?> source) {
 		return iterableToDelimitedString(source, "[ ", " ]", BsonUtils::toJson);
 	}