Can index null values

package.json

@@ -22,7 +22,7 @@
   "dependencies": {
     "async": "~0.2.8",
     "underscore": "~1.4.4",
-    "binary-search-tree": "0.2.1"
+    "binary-search-tree": "0.2.2"
   },
   "devDependencies": {
     "chai": "1.0.x",

test/indexes.test.js

@@ -463,6 +463,13 @@ describe('Indexes', function () {
       idx.insert(doc1);
       idx.insert(doc2);
       idx.insert(doc3);
+
+      assert.deepEqual(idx.getMatching('bloup'), []);
+      assert.deepEqual(idx.getMatching('hello'), [doc1]);
+      assert.deepEqual(idx.getMatching('world'), [doc3]);
+      assert.deepEqual(idx.getMatching('yes'), []);
+      assert.deepEqual(idx.getMatching(undefined), [doc2]);
+
       idx.insert(doc4);
 
       assert.deepEqual(idx.getMatching('bloup'), []);
@@ -472,6 +479,33 @@ describe('Indexes', function () {
       assert.deepEqual(idx.getMatching(undefined), [doc2, doc4]);
     });
 
+    it('Can get all documents for which a field is null', function () {
+      var idx = new Index({ fieldName: 'tf' })
+        , doc1 = { a: 5, tf: 'hello' }
+        , doc2 = { a: 2, tf: null }
+        , doc3 = { a: 8, tf: 'world' }
+        , doc4 = { a: 7, tf: null }
+        ;
+
+      idx.insert(doc1);
+      idx.insert(doc2);
+      idx.insert(doc3);
+
+      assert.deepEqual(idx.getMatching('bloup'), []);
+      assert.deepEqual(idx.getMatching('hello'), [doc1]);
+      assert.deepEqual(idx.getMatching('world'), [doc3]);
+      assert.deepEqual(idx.getMatching('yes'), []);
+      assert.deepEqual(idx.getMatching(null), [doc2]);
+
+      idx.insert(doc4);
+
+      assert.deepEqual(idx.getMatching('bloup'), []);
+      assert.deepEqual(idx.getMatching('hello'), [doc1]);
+      assert.deepEqual(idx.getMatching('world'), [doc3]);
+      assert.deepEqual(idx.getMatching('yes'), []);
+      assert.deepEqual(idx.getMatching(null), [doc2, doc4]);
+    });
+
     it('Can get all documents for a given key in a sparse index, but not unindexed docs (= field undefined)', function () {
       var idx = new Index({ fieldName: 'tf', sparse: true })
         , doc1 = { a: 5, tf: 'hello' }