Fix npe when using source confirmed text query against missing field (#127414)

We should check for the field and statistics actually existing when
checking matches and explanation with `match_only_text` fields

closes: #125635

Author: benwtrent

docs/changelog/127414.yaml

@@ -0,0 +1,5 @@
+pr: 127414
+summary: Fix npe when using source confirmed text query against missing field
+area: Search
+type: bug
+issues: []

modules/mapper-extras/src/main/java/org/elasticsearch/index/mapper/extras/SourceConfirmedTextQuery.java

@@ -267,7 +267,11 @@ public boolean isCacheable(LeafReaderContext ctx) {
             @Override
             public Explanation explain(LeafReaderContext context, int doc) throws IOException {
                 NumericDocValues norms = context.reader().getNormValues(field);
-                RuntimePhraseScorer scorer = (RuntimePhraseScorer) scorerSupplier(context).get(0);
+                ScorerSupplier scorerSupplier = scorerSupplier(context);
+                if (scorerSupplier == null) {
+                    return Explanation.noMatch("No matching phrase");
+                }
+                RuntimePhraseScorer scorer = (RuntimePhraseScorer) scorerSupplier.get(0);
                 if (scorer == null) {
                     return Explanation.noMatch("No matching phrase");
                 }
@@ -277,6 +281,7 @@ public Explanation explain(LeafReaderContext context, int doc) throws IOExceptio
                 }
                 float phraseFreq = scorer.freq();
                 Explanation freqExplanation = Explanation.match(phraseFreq, "phraseFreq=" + phraseFreq);
+                assert simScorer != null;
                 Explanation scoreExplanation = simScorer.explain(freqExplanation, getNormValue(norms, doc));
                 return Explanation.match(
                     scoreExplanation.getValue(),
@@ -321,7 +326,11 @@ public Matches matches(LeafReaderContext context, int doc) throws IOException {
                     Weight innerWeight = in.createWeight(searcher, ScoreMode.COMPLETE_NO_SCORES, 1);
                     return innerWeight.matches(context, doc);
                 }
-                RuntimePhraseScorer scorer = (RuntimePhraseScorer) scorerSupplier(context).get(0L);
+                ScorerSupplier scorerSupplier = scorerSupplier(context);
+                if (scorerSupplier == null) {
+                    return null;
+                }
+                RuntimePhraseScorer scorer = (RuntimePhraseScorer) scorerSupplier.get(0L);
                 if (scorer == null) {
                     return null;
                 }

modules/mapper-extras/src/test/java/org/elasticsearch/index/mapper/extras/SourceConfirmedTextQueryTests.java

@@ -24,6 +24,7 @@
 import org.apache.lucene.queries.spans.SpanTermQuery;
 import org.apache.lucene.search.BooleanClause.Occur;
 import org.apache.lucene.search.BooleanQuery;
+import org.apache.lucene.search.Explanation;
 import org.apache.lucene.search.IndexSearcher;
 import org.apache.lucene.search.MatchNoDocsQuery;
 import org.apache.lucene.search.Matches;
@@ -101,6 +102,26 @@ public void testTerm() throws Exception {
         }
     }
 
+    public void testMissingPhrase() throws Exception {
+        try (Directory dir = newDirectory(); IndexWriter w = new IndexWriter(dir, newIndexWriterConfig(Lucene.STANDARD_ANALYZER))) {
+
+            Document doc = new Document();
+            doc.add(new TextField("body", "a b c b a b c", Store.YES));
+            w.addDocument(doc);
+
+            try (IndexReader reader = DirectoryReader.open(w)) {
+                IndexSearcher searcher = newSearcher(reader);
+                PhraseQuery query = new PhraseQuery("missing_field", "b", "c");
+                Query sourceConfirmedPhraseQuery = new SourceConfirmedTextQuery(query, SOURCE_FETCHER_PROVIDER, Lucene.STANDARD_ANALYZER);
+                Explanation explanation = searcher.explain(sourceConfirmedPhraseQuery, 0);
+                assertFalse(explanation.isMatch());
+
+                Weight weight = searcher.createWeight(query, ScoreMode.COMPLETE, 1);
+                assertNull(weight.matches(getOnlyLeafReader(reader).getContext(), 0));
+            }
+        }
+    }
+
     public void testPhrase() throws Exception {
         try (Directory dir = newDirectory(); IndexWriter w = new IndexWriter(dir, newIndexWriterConfig(Lucene.STANDARD_ANALYZER))) {