diff --git a/convex-benchmarks/src/main/java/convex/benchmarks/ThreadCoordinationBenchmark.java b/convex-benchmarks/src/main/java/convex/benchmarks/ThreadCoordinationBenchmark.java
index 24f56e26f..c7e9de23a 100644
--- a/convex-benchmarks/src/main/java/convex/benchmarks/ThreadCoordinationBenchmark.java
+++ b/convex-benchmarks/src/main/java/convex/benchmarks/ThreadCoordinationBenchmark.java
@@ -21,7 +21,6 @@ public class ThreadCoordinationBenchmark {
 					o = INPUT.take();
 					OUTPUT.put(o);
 				} catch (InterruptedException e) {
-					// TODO Auto-generated catch block
 					e.printStackTrace();
 				}
 			}
diff --git a/convex-core/src/main/java/convex/core/data/AMap.java b/convex-core/src/main/java/convex/core/data/AMap.java
index c0cca1b21..b276bd7d5 100644
--- a/convex-core/src/main/java/convex/core/data/AMap.java
+++ b/convex-core/src/main/java/convex/core/data/AMap.java
@@ -237,7 +237,7 @@ public final V get(Object key) {
 	 * @return Value for the specified key, or the notFound value.
 	 */
 	@SuppressWarnings("unchecked")
-	public final V get(ACell key, ACell notFound) {
+	public V get(ACell key, ACell notFound) {
 		MapEntry<K, V> me = getEntry((K) key);
 		if (me == null) {
 			return (V) notFound;
diff --git a/convex-core/src/main/java/convex/core/data/ARecord.java b/convex-core/src/main/java/convex/core/data/ARecord.java
index 65e57565d..248118a6d 100644
--- a/convex-core/src/main/java/convex/core/data/ARecord.java
+++ b/convex-core/src/main/java/convex/core/data/ARecord.java
@@ -53,8 +53,6 @@ protected ARecord toCanonical() {
 		return true;
 	}
 	
-
-
 	/**
 	 * Gets a vector of keys for this record
 	 * 
@@ -161,7 +159,6 @@ public final AMap<Keyword, ACell> dissoc(ACell key) {
 
 	@Override
 	public MapEntry<Keyword, ACell> getKeyRefEntry(Ref<ACell> keyRef) {
-		// TODO: could maybe be more efficient?
 		return getEntry(keyRef.getValue());
 	}
 
@@ -228,8 +225,16 @@ public boolean print(BlobBuilder sb, long limit) {
 
 	@Override
 	public MapEntry<Keyword, ACell> getEntry(ACell k) {
-		if (!containsKey(k)) return null;
-		return MapEntry.create((Keyword)k,get(k));
+		ACell v=get(k);
+		if ((v==null)&&!containsKey(k)) return null; //if null, need to check if key exists
+		return MapEntry.create((Keyword)k,v);
+	}
+	
+	@Override
+	public ACell get(ACell key, ACell notFound) {
+		ACell v=get(key);
+		if ((v==null)&&!containsKey(key)) return notFound; //if null, need to check if key exists
+		return v;
 	}
 
 	@Override
diff --git a/convex-core/src/main/java/convex/core/data/AccountStatus.java b/convex-core/src/main/java/convex/core/data/AccountStatus.java
index 0070299a9..6528bce3d 100644
--- a/convex-core/src/main/java/convex/core/data/AccountStatus.java
+++ b/convex-core/src/main/java/convex/core/data/AccountStatus.java
@@ -192,7 +192,7 @@ public static AccountStatus read(Blob b, int pos) throws BadFormatException {
 		};		
 		Address controller=null;
 		if ((included&HAS_CONTROLLER)!=0) {
-			controller=Format.read(b, epos); // TODO should be raw Address, save a byte?
+			controller=Format.read(b, epos);
 			epos+=controller.getEncodingLength();
 		}
 		AHashMap<Symbol, ACell> environment = null;
diff --git a/convex-core/src/main/java/convex/core/data/Address.java b/convex-core/src/main/java/convex/core/data/Address.java
index 53cb386e3..960f8dbf1 100644
--- a/convex-core/src/main/java/convex/core/data/Address.java
+++ b/convex-core/src/main/java/convex/core/data/Address.java
@@ -303,7 +303,6 @@ public final int getBytes(byte[] bs, int pos) {
 
 	@Override
 	public long longValue() {
-		// TODO Auto-generated method stub
 		return value;
 	}
 
diff --git a/convex-core/src/main/java/convex/core/data/Cells.java b/convex-core/src/main/java/convex/core/data/Cells.java
index c27912a56..6426aec50 100644
--- a/convex-core/src/main/java/convex/core/data/Cells.java
+++ b/convex-core/src/main/java/convex/core/data/Cells.java
@@ -6,6 +6,7 @@
 import java.util.function.Consumer;
 
 import convex.core.Result;
+import convex.core.data.impl.DummyCell;
 import convex.core.exceptions.ParseException;
 import convex.core.store.AStore;
 import convex.core.store.Stores;
@@ -27,6 +28,8 @@ public class Cells {
 	 */
 	public static final int MAX_BRANCH_COUNT = 68;
 
+	public static final ACell DUMMY = new DummyCell();
+
 	/**
 	 * Equality method allowing for nulls
 	 *
diff --git a/convex-core/src/main/java/convex/core/data/impl/DummyCell.java b/convex-core/src/main/java/convex/core/data/impl/DummyCell.java
new file mode 100644
index 000000000..5221fe609
--- /dev/null
+++ b/convex-core/src/main/java/convex/core/data/impl/DummyCell.java
@@ -0,0 +1,73 @@
+package convex.core.data.impl;
+
+import convex.core.data.ACell;
+import convex.core.data.Tag;
+import convex.core.data.util.BlobBuilder;
+import convex.core.exceptions.InvalidDataException;
+
+/**
+ * A dummy cell implementation, not a valid CVM value
+ */
+public class DummyCell extends ACell {
+
+	@Override
+	public int estimatedEncodingSize() {
+		return 1;
+	}
+
+	@Override
+	public void validateCell() throws InvalidDataException {
+		throw new InvalidDataException("This is a dummy value",this);
+	}
+
+	@Override
+	protected byte getTag() {
+		return Tag.ILLEGAL;
+	}
+
+	@Override
+	public boolean equals(ACell a) {
+		return this==a;
+	}
+
+	@Override
+	public int encode(byte[] bs, int pos) {
+		bs[pos++]=Tag.ILLEGAL;
+		return pos;
+	}
+	
+	@Override
+	protected int encodeRaw(byte[] bs, int pos) {
+		// Nothing to encode
+		return pos;
+	}
+
+	@Override
+	public boolean isCanonical() {
+		return true;
+	}
+
+	@Override
+	protected ACell toCanonical() {
+		return this;
+	}
+
+	@Override
+	public boolean isCVMValue() {
+		return false;
+	}
+
+	@Override
+	public boolean isDataValue() {
+		return false;
+	}
+
+	@Override
+	public boolean print(BlobBuilder sb, long limit) {
+		sb.append("DUMMY");
+		return sb.check(limit);
+	}
+
+
+
+}