#vulnerable code 
                             private void mapOneToMany(Object instance, Class<?> valueType, Object values, String relationshipType, String relationshipDirection) {

		ClassInfo classInfo = metadata.classInfo(instance);

		RelationalWriter writer = entityAccessStrategy.getIterableWriter(classInfo, valueType, relationshipType, relationshipDirection);
		if (writer != null) {
			if (writer.type().isArray() || Iterable.class.isAssignableFrom(writer.type())) {
				RelationalReader reader = entityAccessStrategy.getIterableReader(classInfo, valueType, relationshipType, relationshipDirection);
				Object currentValues;
				if (reader != null) {
					currentValues = reader.read(instance);
					if (writer.type().isArray()) {
						values = EntityAccess.merge(writer.type(), (Iterable<?>) values, (Object[]) currentValues, valueType);
					} else {
						values = EntityAccess.merge(writer.type(), (Iterable<?>) values, (Collection) currentValues, valueType);
					}
				}
			}
			writer.write(instance, values);
			return;
		}
		// this is not necessarily an error. but we can't tell.
		logger.debug("Unable to map iterable of type: {} onto property of {}", valueType, classInfo.name());
	} 
                            #location 23 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                             private void mapOneToMany(Object instance, Class<?> valueType, Object values, String relationshipType, String relationshipDirection) {

		ClassInfo classInfo = metadata.classInfo(instance);

		RelationalWriter writer = EntityAccessManager.getIterableWriter(classInfo, valueType, relationshipType, relationshipDirection);
		if (writer != null) {
			if (writer.type().isArray() || Iterable.class.isAssignableFrom(writer.type())) {
				RelationalReader reader = EntityAccessManager.getIterableReader(classInfo, valueType, relationshipType, relationshipDirection);
				Object currentValues;
				if (reader != null) {
					currentValues = reader.read(instance);
					if (writer.type().isArray()) {
						values = EntityAccess.merge(writer.type(), (Iterable<?>) values, (Object[]) currentValues, valueType);
					} else {
						values = EntityAccess.merge(writer.type(), (Iterable<?>) values, (Collection) currentValues, valueType);
					}
				}
			}
			writer.write(instance, values);
			return;
		}
		// this is not necessarily an error. but we can't tell.
		logger.debug("Unable to map iterable of type: {} onto property of {}", valueType, classInfo.name());
	}