fix null comparisons in sqlitedb backend

associated test added and passing

IPython/parallel/controller/sqlitedb.py

@@ -293,7 +293,7 b' class SQLiteDB(BaseDB):'
                         op, join = op
 
                     if value is None and op in null_operators:
-                            expr = "%s %s"%null_operators[op]
+                        expr = "%s %s" % (name, null_operators[op])
                     else:
                         expr = "%s %s ?"%(name, op)
                         if isinstance(value, (tuple,list)):
@@ -308,7 +308,7 b' class SQLiteDB(BaseDB):'
             else:
                 # it's an equality check
                 if sub_check is None:
-                    expressions.append("%s IS NULL")
+                    expressions.append("%s IS NULL" % name)
                 else:
                     expressions.append("%s = ?"%name)
                     args.append(sub_check)

IPython/parallel/tests/test_db.py

@@ -170,6 +170,18 b' class TestDictBackend(TestCase):'
         self.db.drop_matching_records(query)
         recs = self.db.find_records(query)
         self.assertEquals(len(recs), 0)
+    
+    def test_null(self):
+        """test None comparison queries"""
+        msg_ids = self.load_records(10)
+
+        query = {'msg_id' : None}
+        recs = self.db.find_records(query)
+        self.assertEquals(len(recs), 0)
+
+        query = {'msg_id' : {'$ne' : None}}
+        recs = self.db.find_records(query)
+        self.assertTrue(len(recs) >= 10)
 
 
 class TestSQLiteBackend(TestDictBackend):