add default empty constructor for hadoop version
diff --git a/genomix/genomix-data/src/main/java/edu/uci/ics/genomix/type/KmerBytesWritable.java b/genomix/genomix-data/src/main/java/edu/uci/ics/genomix/type/KmerBytesWritable.java
index 59159e9..5d1cc11 100644
--- a/genomix/genomix-data/src/main/java/edu/uci/ics/genomix/type/KmerBytesWritable.java
+++ b/genomix/genomix-data/src/main/java/edu/uci/ics/genomix/type/KmerBytesWritable.java
@@ -32,11 +32,32 @@
     /**
 	 * 
 	 */
-	private static final long serialVersionUID = 1L;
-	protected int size;
+    private static final long serialVersionUID = 1L;
+    private static final byte[] EMPTY_BYTES = {};
+
+    protected int size;
     protected byte[] bytes;
     protected int kmerlength;
 
+    @Deprecated
+    public KmerBytesWritable() {
+        this(0, EMPTY_BYTES);
+    }
+
+    public KmerBytesWritable(int k, byte[] storage) {
+        this.kmerlength = k;
+        if (k > 0){
+            this.size = KmerUtil.getByteNumFromK(kmerlength);
+            this.bytes = storage;
+            if (this.bytes.length < size){
+                throw new ArrayIndexOutOfBoundsException("Storage is smaller than required space for kmerlength:k");
+            }
+        }else{
+            this.bytes = storage;
+            this.size = 0;
+        }
+    }
+
     /**
      * Initial Kmer space by kmerlength
      * 
@@ -213,7 +234,7 @@
     public void readFields(DataInput in) throws IOException {
         this.kmerlength = in.readInt();
         this.size = KmerUtil.getByteNumFromK(kmerlength);
-        if ( this.bytes.length < this.size){
+        if (this.bytes.length < this.size) {
             this.bytes = new byte[this.size];
         }
         in.readFully(bytes, 0, size);
diff --git a/genomix/genomix-data/src/main/java/edu/uci/ics/genomix/type/VKmerBytesWritable.java b/genomix/genomix-data/src/main/java/edu/uci/ics/genomix/type/VKmerBytesWritable.java
index 3319cad..493191a 100644
--- a/genomix/genomix-data/src/main/java/edu/uci/ics/genomix/type/VKmerBytesWritable.java
+++ b/genomix/genomix-data/src/main/java/edu/uci/ics/genomix/type/VKmerBytesWritable.java
@@ -7,10 +7,14 @@
      * 
      */
     private static final long serialVersionUID = 1L;
-    public static final int DEFAULT_KMER_LENGTH = 21;
 
+    @Deprecated
     public VKmerBytesWritable() {
-        this(DEFAULT_KMER_LENGTH);
+        super();
+    }
+    
+    public VKmerBytesWritable(int k, byte[] storage){
+        super(k, storage);
     }
 
     public VKmerBytesWritable(int k) {