#vulnerable code 
                                public Long nativeId(Object entity) {
        ClassInfo classInfo = metaData.classInfo(entity);
        generateIdIfNecessary(entity, classInfo);

        if (classInfo.hasIdentityField()) {
            return EntityUtils.identity(entity, metaData);
        } else {
            FieldInfo fieldInfo = classInfo.primaryIndexField();
            Object primaryId = fieldInfo.readProperty(entity);

            if (primaryId == null) {
                throw new MappingException("Field with primary id is null for entity " + entity);
            }
            LabelPrimaryId key = new LabelPrimaryId(classInfo, primaryId);
            Long graphId = primaryIdToNativeId.get(key);
            if (graphId == null) {
                graphId = EntityUtils.nextRef();
                primaryIdToNativeId.put(key, graphId);
            }
            return graphId;
        }
    } 
                            #location 3 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                public Long nativeId(Object entity) {
        ClassInfo classInfo = metaData.classInfo(entity);

        if (classInfo == null) {
            throw new IllegalArgumentException("Class " + entity.getClass() + " is not a valid entity class. "
                + "Please check the entity mapping.");
        }

        generateIdIfNecessary(entity, classInfo);
        if (classInfo.hasIdentityField()) {
            return EntityUtils.identity(entity, metaData);
        } else {
            FieldInfo fieldInfo = classInfo.primaryIndexField();
            Object primaryId = fieldInfo.readProperty(entity);

            if (primaryId == null) {
                throw new MappingException("Field with primary id is null for entity " + entity);
            }
            LabelPrimaryId key = new LabelPrimaryId(classInfo, primaryId);
            Long graphId = primaryIdToNativeId.get(key);
            if (graphId == null) {
                graphId = EntityUtils.nextRef();
                primaryIdToNativeId.put(key, graphId);
            }
            return graphId;
        }
    }