[BUG] NPE on SLTR query when feature set doesn't exist

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What is the bug?

A clear and concise description of the bug.

NPE on SLTR query when feature set doesn't exist

How can one reproduce the bug?

Steps to reproduce the behavior.

1. Create tmdb index

2. Search on tmdb index with SLTR query

POST tmdb/_search
{
    "query": {
        "bool": {
            "filter": [
                {
                    "terms": {
                        "_id": ["7555", "1370", "1369"]
                    }
                },
                {
                    "sltr": {
                        "_name": "logged_featureset",
                        "featureset": "more_movie_features",
                        "params": {
                            "keywords": "rambo"
                        }
                }}
            ]
        }
    },
    "ext": {
        "ltr_log": {
            "log_specs": {
                "name": "log_entry1",
                "named_query": "logged_featureset"
            }
        }
    }
}

{
  "error": {
    "root_cause": [
      {
        "type": "query_shard_exception",
        "reason": "failed to create query: java.lang.NullPointerException: Cannot invoke \"com.o19s.es.ltr.feature.store.StoredFeatureSet.optimize()\" because the return value of \"com.o19s.es.ltr.feature.store.index.IndexFeatureStore.getAndParse(String, java.lang.Class, String)\" is null",
        "index": "tmdb",
        "index_uuid": "Vq8x0os1RvqSmjCqBrKXqQ"
      }
    ],
    "type": "search_phase_execution_exception",
    "reason": "all shards failed",
    "phase": "query",
    "grouped": true,
    "failed_shards": [
      {
        "shard": 0,
        "index": "tmdb",
        "node": "-vRjBvEwSIimAr9UL-3NGg",
        "reason": {
          "type": "query_shard_exception",
          "reason": "failed to create query: java.lang.NullPointerException: Cannot invoke \"com.o19s.es.ltr.feature.store.StoredFeatureSet.optimize()\" because the return value of \"com.o19s.es.ltr.feature.store.index.IndexFeatureStore.getAndParse(String, java.lang.Class, String)\" is null",
          "index": "tmdb",
          "index_uuid": "Vq8x0os1RvqSmjCqBrKXqQ",
          "caused_by": {
            "type": "i_o_exception",
            "reason": "java.lang.NullPointerException: Cannot invoke \"com.o19s.es.ltr.feature.store.StoredFeatureSet.optimize()\" because the return value of \"com.o19s.es.ltr.feature.store.index.IndexFeatureStore.getAndParse(String, java.lang.Class, String)\" is null",
            "caused_by": {
              "type": "null_pointer_exception",
              "reason": "Cannot invoke \"com.o19s.es.ltr.feature.store.StoredFeatureSet.optimize()\" because the return value of \"com.o19s.es.ltr.feature.store.index.IndexFeatureStore.getAndParse(String, java.lang.Class, String)\" is null"
            }
          }
        }
      }
    ]
  },
  "status": 400
}

What is the expected behavior?

A clear and concise description of what you expected to happen.

opensearch-learning-to-rank-base/src/main/java/com/o19s/es/ltr/feature/store/index/Caches.java

Lines 136 to 149 in 9477c52

	private <E> E cacheLoad(CacheKey key, Cache<CacheKey, E> cache,
	CheckedFunction<String, E, IOException> loader) throws IOException {
	try {
	return cache.computeIfAbsent(key, (k) -> {
	E elt = loader.apply(k.getId());
	if (elt != null) {
	onAdd(k, elt);
	}
	return elt;
	});
	} catch (ExecutionException e) {
	throw new IOException(e.getMessage(), e.getCause());
	}
	}

Info contains 1. cachekey is a feature or a feature set 2. provide error msg like "Feature (set) does not exist"

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[2023-12-13T02:37:03,401][DEBUG][o.o.a.s.TransportSearchAction] [da91b284ed8b1c1b21b4aa288bbf9072] #[org.opensearch.index.query.QueryShardException,java.io.IOException,java.lang.NullPointerException]#All shards failed for phase: [query]
[tmdb/xinVDIeHR7CzbCkTgWnoSg] QueryShardException[failed to create query: java.lang.NullPointerException: Cannot invoke "com.o19s.es.ltr.feature.store.StoredFeatureSet.optimize()" because the return value of "com.o19s.es.ltr.feature.store.index.IndexFeatureStore.getAndParse(String, java.lang.Class, String)" is null]; nested: IOException[java.lang.NullPointerException: Cannot invoke "com.o19s.es.ltr.feature.store.StoredFeatureSet.optimize()" because the return value of "com.o19s.es.ltr.feature.store.index.IndexFeatureStore.getAndParse(String, java.lang.Class, String)" is null]; nested: NullPointerException[Cannot invoke "com.o19s.es.ltr.feature.store.StoredFeatureSet.optimize()" because the return value of "com.o19s.es.ltr.feature.store.index.IndexFeatureStore.getAndParse(String, java.lang.Class, String)" is null];
        at org.opensearch.index.query.QueryShardContext.toQuery(QueryShardContext.java:483)
        at org.opensearch.index.query.QueryShardContext.toQuery(QueryShardContext.java:466)
        at org.opensearch.search.SearchService.parseSource(SearchService.java:1238)
        at org.opensearch.search.SearchService.createContext(SearchService.java:985)
        at org.opensearch.search.SearchService.executeQueryPhase(SearchService.java:593)
        at org.opensearch.search.SearchService$2.lambda$onResponse$0(SearchService.java:566)
        at org.opensearch.action.ActionRunnable.lambda$supply$0(ActionRunnable.java:74)
        at org.opensearch.action.ActionRunnable$2.doRun(ActionRunnable.java:89)
        at org.opensearch.common.util.concurrent.AbstractRunnable.run(AbstractRunnable.java:52)
        at org.opensearch.threadpool.TaskAwareRunnable.doRun(TaskAwareRunnable.java:78)
        at org.opensearch.common.util.concurrent.AbstractRunnable.run(AbstractRunnable.java:52)
        at org.opensearch.common.util.concurrent.TimedRunnable.doRun(TimedRunnable.java:59)
        at org.opensearch.common.util.concurrent.ThreadContext$ContextPreservingAbstractRunnable.doRun(ThreadContext.java:917)
        at org.opensearch.common.util.concurrent.AbstractRunnable.run(AbstractRunnable.java:52)
        at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136)
        at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)
        at java.base/java.lang.Thread.run(Thread.java:833)
Caused by: java.io.IOException: java.lang.NullPointerException: Cannot invoke "com.o19s.es.ltr.feature.store.StoredFeatureSet.optimize()" because the return value of "com.o19s.es.ltr.feature.store.index.IndexFeatureStore.getAndParse(String, java.lang.Class, String)" is null
        at com.o19s.es.ltr.feature.store.index.Caches.cacheLoad(Caches.java:147)
        at com.o19s.es.ltr.feature.store.index.Caches.loadFeatureSet(Caches.java:129)
        at com.o19s.es.ltr.feature.store.index.CachedFeatureStore.loadSet(CachedFeatureStore.java:51)
        at com.o19s.es.ltr.query.StoredLtrQueryBuilder.doToQuery(StoredLtrQueryBuilder.java:175)
        at com.o19s.es.ltr.query.StoredLtrQueryBuilder.doToQuery(StoredLtrQueryBuilder.java:51)
        at org.opensearch.index.query.AbstractQueryBuilder.toQuery(AbstractQueryBuilder.java:117)
        at org.opensearch.index.query.BoolQueryBuilder.addBooleanClauses(BoolQueryBuilder.java:346)
        at org.opensearch.index.query.BoolQueryBuilder.doToQuery(BoolQueryBuilder.java:329)
        at org.opensearch.index.query.AbstractQueryBuilder.toQuery(AbstractQueryBuilder.java:117)
        at org.opensearch.index.query.QueryShardContext.lambda$toQuery$3(QueryShardContext.java:467)
        at org.opensearch.index.query.QueryShardContext.toQuery(QueryShardContext.java:479)
        ... 16 more
Caused by: java.lang.NullPointerException: Cannot invoke "com.o19s.es.ltr.feature.store.StoredFeatureSet.optimize()" because the return value of "com.o19s.es.ltr.feature.store.index.IndexFeatureStore.getAndParse(String, java.lang.Class, String)" is null
        at com.o19s.es.ltr.feature.store.index.IndexFeatureStore.loadSet(IndexFeatureStore.java:123)
        at com.o19s.es.ltr.feature.store.index.Caches.lambda$cacheLoad$7(Caches.java:140)
        at org.opensearch.common.cache.Cache.computeIfAbsent(Cache.java:461)
        at com.o19s.es.ltr.feature.store.index.Caches.cacheLoad(Caches.java:139)
        ... 26 more

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opensearch-learning-to-rank-base/src/main/java/com/o19s/es/ltr/feature/store/index/IndexFeatureStore.java

Line 198 in 9477c52

return () -> clientSupplier.get().prepareGet(index, id).get();

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Post some debugging logs here

[2023-12-13T16:11:24,846][INFO ][c.o.e.l.f.s.i.IndexFeatureStore] [88665a1d4119.ant.amazon.com] internalGet index: .ltrstore
[2023-12-13T16:11:24,847][INFO ][c.o.e.l.f.s.i.IndexFeatureStore] [88665a1d4119.ant.amazon.com] internalGet id: featureset-aaa_more_movie_features
[2023-12-13T16:11:24,849][INFO ][c.o.e.l.f.s.i.IndexFeatureStore] [88665a1d4119.ant.amazon.com] getAndParse(): {"_index":".ltrstore","_id":"featureset-aaa_more_movie_features","found":false}

Instead of return null, we should handle this more gracefully.

opensearch-learning-to-rank-base/src/main/java/com/o19s/es/ltr/feature/store/index/IndexFeatureStore.java

Lines 176 to 199 in 9477c52

	public <E extends StorableElement> E getAndParse(String name, Class<E> eltClass, String type) throws IOException {
	GetResponse response = internalGet(generateId(type, name)).get();
	if (response.isExists()) {
	return parse(eltClass, type, response.getSourceAsBytes());
	} else {
	return null;
	}
	}
	public GetResponse getFeature(String name) {
	return internalGet(generateId(StoredFeature.TYPE, name)).get();
	}
	public GetResponse getFeatureSet(String name) {
	return internalGet(generateId(StoredFeatureSet.TYPE, name)).get();
	}
	public GetResponse getModel(String name) {
	return internalGet(generateId(StoredLtrModel.TYPE, name)).get();
	}
	private Supplier<GetResponse> internalGet(String id) {
	return () -> clientSupplier.get().prepareGet(index, id).get();
	}

[epugh]

Good candidate for @JohannesDaniel