From 1452d3fac5f2500cda0439a45294b9382c8c2d42 Mon Sep 17 00:00:00 2001
From: Ross Lawley <ross.lawley@gmail.com>
Date: Mon, 11 Jul 2011 16:50:31 +0100
Subject: [PATCH] Fixed item_frequency methods to handle null values

[fixes #216]
---
 mongoengine/queryset.py | 13 ++++++++-----
 tests/queryset.py       | 22 ++++++++++++++++++++++
 2 files changed, 30 insertions(+), 5 deletions(-)

diff --git a/mongoengine/queryset.py b/mongoengine/queryset.py
index 6b110ff0..d533736b 100644
--- a/mongoengine/queryset.py
+++ b/mongoengine/queryset.py
@@ -1435,7 +1435,7 @@ class QuerySet(object):
                 path = '{{~%(field)s}}'.split('.');
                 field = this;
                 for (p in path) { field = field[path[p]]; }
-                if (field.constructor == Array) {
+                if (field && field.constructor == Array) {
                     field.forEach(function(item) {
                         emit(item, 1);
                     });
@@ -1481,7 +1481,7 @@ class QuerySet(object):
                     db[collection].find(query).forEach(function(doc) {
                         field = doc;
                         for (p in path) { field = field[path[p]]; }
-                        if (field.constructor == Array) {
+                        if (field && field.constructor == Array) {
                             total += field.length;
                         } else {
                             total++;
@@ -1497,7 +1497,7 @@ class QuerySet(object):
                 db[collection].find(query).forEach(function(doc) {
                     field = doc;
                     for (p in path) { field = field[path[p]]; }
-                    if (field.constructor == Array) {
+                    if (field && field.constructor == Array) {
                         field.forEach(function(item) {
                             frequencies[item] = inc + (isNaN(frequencies[item]) ? 0: frequencies[item]);
                         });
@@ -1509,8 +1509,11 @@ class QuerySet(object):
                 return frequencies;
             }
         """
-
-        return self.exec_js(freq_func, field, normalize=normalize)
+        data = self.exec_js(freq_func, field, normalize=normalize)
+        if 'undefined' in data:
+            data[None] = data['undefined']
+            del(data['undefined'])
+        return data
 
     def __repr__(self):
         limit = REPR_OUTPUT_SIZE + 1
diff --git a/tests/queryset.py b/tests/queryset.py
index c0860b5c..e21db0fa 100644
--- a/tests/queryset.py
+++ b/tests/queryset.py
@@ -1781,6 +1781,28 @@ class QuerySetTest(unittest.TestCase):
         test_assertions(exec_js)
         test_assertions(map_reduce)
 
+    def test_item_frequencies_null_values(self):
+
+        class Person(Document):
+            name = StringField()
+            city = StringField()
+
+        Person.drop_collection()
+
+        Person(name="Wilson Snr", city="CRB").save()
+        Person(name="Wilson Jr").save()
+
+        freq = Person.objects.item_frequencies('city')
+        self.assertEquals(freq, {'CRB': 1.0, None: 1.0})
+        freq = Person.objects.item_frequencies('city', normalize=True)
+        self.assertEquals(freq, {'CRB': 0.5, None: 0.5})
+
+
+        freq = Person.objects.item_frequencies('city', map_reduce=True)
+        self.assertEquals(freq, {'CRB': 1.0, None: 1.0})
+        freq = Person.objects.item_frequencies('city', normalize=True, map_reduce=True)
+        self.assertEquals(freq, {'CRB': 0.5, None: 0.5})
+
     def test_average(self):
         """Ensure that field can be averaged correctly.
         """