diff --git a/src/main/java/it/cavallium/strangedb/database/references/DatabaseReferencesMetadataCache.java b/src/main/java/it/cavallium/strangedb/database/references/DatabaseReferencesMetadataCache.java
index 9785d2e..e474606 100644
--- a/src/main/java/it/cavallium/strangedb/database/references/DatabaseReferencesMetadataCache.java
+++ b/src/main/java/it/cavallium/strangedb/database/references/DatabaseReferencesMetadataCache.java
@@ -81,13 +81,14 @@ public class DatabaseReferencesMetadataCache {
 		if (closed) throw new IOException("Cache already closed!");
 		lock.writeLock().lock();
 		try {
-			for (int i = 0; i < references.length; i++) {
-				if (cleanerIds[i] == 0) {
-					throw new IOException("Null cleaner id");
-				}
-			}
 			Long2LongMap referencesBlocksToAdd = new Long2LongLinkedOpenHashMap(references, blockIds, 0.5f);
 			Long2ByteMap referencesCleanersToAdd = new Long2ByteLinkedOpenHashMap(references, cleanerIds, 0.5f);
+			for (int i = 0; i < references.length; i++) {
+				if (cleanerIds[i] == 0) {
+					referencesBlocksToAdd.remove(references[i]);
+					referencesCleanersToAdd.remove(references[i]);
+				}
+			}
 			references2Blocks.putAll(referencesBlocksToAdd);
 			referencesCleaners.putAll(referencesCleanersToAdd);
 			flush();