private void check(String modelName) throws IllegalStateException {
            for (int i = 0; i < keys.size(); i++) {
                final ModelColumn modelColumn = keys.get(i);
                if (modelColumn == null) {
                    throw new IllegalStateException("sharding key index=" + i + " is missing in " + modelName);
                }
            }
        }
@param modelName model name of the entity
@throws IllegalStateException if sharding key indices are not continuous
oap-server/server-core/src/main/java/org/apache/skywalking/oap/server/core/storage/model/StorageModels.java