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diff --git a/subprojects/viatra-runtime-rete/src/main/java/tools/refinery/viatra/runtime/rete/index/MemoryNullIndexer.java b/subprojects/viatra-runtime-rete/src/main/java/tools/refinery/viatra/runtime/rete/index/MemoryNullIndexer.java
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+++ b/subprojects/viatra-runtime-rete/src/main/java/tools/refinery/viatra/runtime/rete/index/MemoryNullIndexer.java
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+/*******************************************************************************
+ * Copyright (c) 2004-2008 Gabor Bergmann and Daniel Varro
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License v. 2.0 which is available at
+ * http://www.eclipse.org/legal/epl-v20.html.
+ * 
+ * SPDX-License-Identifier: EPL-2.0
+ *******************************************************************************/
+
+package tools.refinery.viatra.runtime.rete.index;
+
+import java.util.Collection;
+import java.util.List;
+
+import tools.refinery.viatra.runtime.matchers.tuple.Tuple;
+import tools.refinery.viatra.runtime.rete.network.Receiver;
+import tools.refinery.viatra.runtime.rete.network.ReteContainer;
+import tools.refinery.viatra.runtime.rete.network.Supplier;
+
+/**
+ * Defines a trivial indexer that projects the contents of a memory-equipped node to the empty tuple, and can therefore
+ * save space. Can only exist in connection with a memory, and must be operated by another node. Do not attach parents
+ * directly!
+ * 
+ * @author Gabor Bergmann
+ * @noimplement Rely on the provided implementations
+ * @noreference Use only via standard Node and Indexer interfaces
+ * @noinstantiate This class is not intended to be instantiated by clients.
+ */
+public class MemoryNullIndexer extends NullIndexer {
+
+    Collection<Tuple> memory;
+
+    /**
+     * @param reteContainer
+     * @param tupleWidth
+     *            the width of the tuples of memoryNode
+     * @param memory
+     *            the memory whose contents are to be null-indexed
+     * @param parent
+     *            the parent node that owns the memory
+     */
+    public MemoryNullIndexer(ReteContainer reteContainer, int tupleWidth, Collection<Tuple> memory,
+            Supplier parent, Receiver activeNode, List<ListenerSubscription> sharedSubscriptionList) {
+        super(reteContainer, tupleWidth, parent, activeNode, sharedSubscriptionList);
+        this.memory = memory;
+    }
+
+    @Override
+    protected Collection<Tuple> getTuples() {
+        return this.memory;
+    }
+
+}