diff --git a/lucene/core/src/java/org/apache/lucene/util/BitDocIdSet.java b/lucene/core/src/java/org/apache/lucene/util/BitDocIdSet.java
index 0502b70f6afd..0bab9ad7eb13 100644
--- a/lucene/core/src/java/org/apache/lucene/util/BitDocIdSet.java
+++ b/lucene/core/src/java/org/apache/lucene/util/BitDocIdSet.java
@@ -16,7 +16,6 @@
  */
 package org.apache.lucene.util;
 
-import java.io.IOException;
 import org.apache.lucene.search.DocIdSet;
 import org.apache.lucene.search.DocIdSetIterator;
 
@@ -58,22 +57,6 @@ public DocIdSetIterator iterator() {
     return new BitSetIterator(set, cost);
   }
 
-  /**
-   * Provides a {@link Bits} interface for random access to matching documents.
-   *
-   * @return {@code null}, if this {@code DocIdSet} does not support random access. In contrast to
-   *     {@link #iterator()}, a return value of {@code null} <b>does not</b> imply that no documents
-   *     match the filter! The default implementation does not provide random access, so you only
-   *     need to implement this method if your DocIdSet can guarantee random access to every docid
-   *     in O(1) time without external disk access (as {@link Bits} interface cannot throw {@link
-   *     IOException}). This is generally true for bit sets like {@link
-   *     org.apache.lucene.util.FixedBitSet}, which return itself if they are used as {@code
-   *     DocIdSet}.
-   */
-  public BitSet bits() {
-    return set;
-  }
-
   @Override
   public long ramBytesUsed() {
     return BASE_RAM_BYTES_USED + set.ramBytesUsed();
diff --git a/lucene/core/src/test/org/apache/lucene/util/TestFixedBitDocIdSet.java b/lucene/core/src/test/org/apache/lucene/util/TestFixedBitDocIdSet.java
index 422d209d1647..dd31f41d76ac 100644
--- a/lucene/core/src/test/org/apache/lucene/util/TestFixedBitDocIdSet.java
+++ b/lucene/core/src/test/org/apache/lucene/util/TestFixedBitDocIdSet.java
@@ -16,9 +16,7 @@
  */
 package org.apache.lucene.util;
 
-import java.io.IOException;
 import java.util.BitSet;
-import org.apache.lucene.search.DocIdSetIterator;
 import org.apache.lucene.tests.util.BaseDocIdSetTestCase;
 
 public class TestFixedBitDocIdSet extends BaseDocIdSetTestCase<BitDocIdSet> {
@@ -31,25 +29,4 @@ public BitDocIdSet copyOf(BitSet bs, int length) {
     }
     return new BitDocIdSet(set);
   }
-
-  @Override
-  public void assertEquals(int numBits, BitSet ds1, BitDocIdSet ds2) throws IOException {
-    super.assertEquals(numBits, ds1, ds2);
-    // bits()
-    final Bits bits = ds2.bits();
-    if (bits != null) {
-      // test consistency between bits and iterator
-      DocIdSetIterator it2 = ds2.iterator();
-      for (int previousDoc = -1, doc = it2.nextDoc(); ; previousDoc = doc, doc = it2.nextDoc()) {
-        final int max = doc == DocIdSetIterator.NO_MORE_DOCS ? bits.length() : doc;
-        for (int i = previousDoc + 1; i < max; ++i) {
-          assertFalse(bits.get(i));
-        }
-        if (doc == DocIdSetIterator.NO_MORE_DOCS) {
-          break;
-        }
-        assertTrue(bits.get(doc));
-      }
-    }
-  }
 }
diff --git a/lucene/core/src/test/org/apache/lucene/util/TestSparseFixedBitDocIdSet.java b/lucene/core/src/test/org/apache/lucene/util/TestSparseFixedBitDocIdSet.java
index e79a3b8e72bc..42489c31cd60 100644
--- a/lucene/core/src/test/org/apache/lucene/util/TestSparseFixedBitDocIdSet.java
+++ b/lucene/core/src/test/org/apache/lucene/util/TestSparseFixedBitDocIdSet.java
@@ -16,7 +16,6 @@
  */
 package org.apache.lucene.util;
 
-import java.io.IOException;
 import java.util.ArrayList;
 import java.util.BitSet;
 import java.util.Collections;
@@ -47,13 +46,4 @@ public BitDocIdSet copyOf(BitSet bs, int length) {
     }
     return new BitDocIdSet(set, set.approximateCardinality());
   }
-
-  @Override
-  public void assertEquals(int numBits, BitSet ds1, BitDocIdSet ds2) throws IOException {
-    for (int i = 0; i < numBits; ++i) {
-      assertEquals(ds1.get(i), ds2.bits().get(i));
-    }
-    assertEquals(ds1.cardinality(), ds2.bits().cardinality());
-    super.assertEquals(numBits, ds1, ds2);
-  }
 }
diff --git a/lucene/join/src/java/org/apache/lucene/search/join/QueryBitSetProducer.java b/lucene/join/src/java/org/apache/lucene/search/join/QueryBitSetProducer.java
index 5539320123cf..ac866fe013d0 100644
--- a/lucene/join/src/java/org/apache/lucene/search/join/QueryBitSetProducer.java
+++ b/lucene/join/src/java/org/apache/lucene/search/join/QueryBitSetProducer.java
@@ -25,19 +25,17 @@
 import org.apache.lucene.index.LeafReader;
 import org.apache.lucene.index.LeafReaderContext;
 import org.apache.lucene.index.ReaderUtil;
-import org.apache.lucene.search.DocIdSet;
 import org.apache.lucene.search.IndexSearcher;
 import org.apache.lucene.search.Query;
 import org.apache.lucene.search.Scorer;
 import org.apache.lucene.search.Weight;
-import org.apache.lucene.util.BitDocIdSet;
 import org.apache.lucene.util.BitSet;
+import org.apache.lucene.util.FixedBitSet;
 
 /** A {@link BitSetProducer} that wraps a query and caches matching {@link BitSet}s per segment. */
 public class QueryBitSetProducer implements BitSetProducer {
   private final Query query;
-  final Map<IndexReader.CacheKey, DocIdSet> cache =
-      Collections.synchronizedMap(new WeakHashMap<>());
+  final Map<IndexReader.CacheKey, BitSet> cache = Collections.synchronizedMap(new WeakHashMap<>());
 
   /**
    * Wraps another query's result and caches it into bitsets.
@@ -57,16 +55,18 @@ public Query getQuery() {
     return query;
   }
 
+  private static final BitSet SENTINEL = new FixedBitSet(0);
+
   @Override
   public BitSet getBitSet(LeafReaderContext context) throws IOException {
     final LeafReader reader = context.reader();
     final IndexReader.CacheHelper cacheHelper = reader.getCoreCacheHelper();
 
-    DocIdSet docIdSet = null;
+    BitSet bitSet = null;
     if (cacheHelper != null) {
-      docIdSet = cache.get(cacheHelper.getKey());
+      bitSet = cache.get(cacheHelper.getKey());
     }
-    if (docIdSet == null) {
+    if (bitSet == null) {
       final IndexReaderContext topLevelContext = ReaderUtil.getTopLevelContext(context);
       final IndexSearcher searcher = new IndexSearcher(topLevelContext);
       searcher.setQueryCache(null);
@@ -77,15 +77,15 @@ public BitSet getBitSet(LeafReaderContext context) throws IOException {
       final Scorer s = weight.scorer(context);
 
       if (s == null) {
-        docIdSet = DocIdSet.EMPTY;
+        bitSet = SENTINEL;
       } else {
-        docIdSet = new BitDocIdSet(BitSet.of(s.iterator(), context.reader().maxDoc()));
+        bitSet = BitSet.of(s.iterator(), context.reader().maxDoc());
       }
       if (cacheHelper != null) {
-        cache.put(cacheHelper.getKey(), docIdSet);
+        cache.put(cacheHelper.getKey(), bitSet);
       }
     }
-    return docIdSet == DocIdSet.EMPTY ? null : ((BitDocIdSet) docIdSet).bits();
+    return bitSet == SENTINEL ? null : bitSet;
   }
 
   @Override