Fixed bug that raised an error for a null value

lib/model.js

@@ -44,7 +44,7 @@ function checkObject (obj) {
     });
   }
 
-  if (typeof obj === 'object') {
+  if (typeof obj === 'object' && obj !== null) {
     Object.keys(obj).forEach(function (k) {
       checkKey(k, obj[k]);
       checkObject(obj[k]);

package.json

@@ -1,6 +1,6 @@
 {
   "name": "nedb",
-  "version": "0.7.3",
+  "version": "0.7.4",
   "author": {
     "name": "tldr.io",
     "email": "hello@tldr.io"

test/model.test.js

@@ -159,6 +159,12 @@ describe('Model', function () {
       // Recursive behaviour testing done in the above test on $ signs
     });
 
+    it('Properties with a null value dont trigger an error', function () {
+      var obj = { prop: null };
+
+      model.checkObject(obj);
+    });
+
   });   // ==== End of 'Object checking' ==== //