Fix get_many to work with an empty array

Instead of raising an exception it should return an empty dict

This is the same behaviour that the default Django cache backends have.

redis_cache/backends/base.py

@@ -302,12 +302,14 @@ class BaseRedisCache(BaseCache):
         recovered_data = {}
         map_keys = dict(zip(versioned_keys, original_keys))
 
-        results = client.mget(versioned_keys)
-
-        for key, value in zip(versioned_keys, results):
-            if value is None:
-                continue
-            recovered_data[map_keys[key]] = self.get_value(value)
+        # Only try to mget if we actually received any keys to get
+        if map_keys:
+            results = client.mget(versioned_keys)
+
+            for key, value in zip(versioned_keys, results):
+                if value is None:
+                    continue
+                recovered_data[map_keys[key]] = self.get_value(value)
 
         return recovered_data
 

tests/testapp/tests/base_tests.py

@@ -176,6 +176,9 @@ class BaseRedisTestCase(SetupMixin):
         self.assertEqual(self.cache.get_many(['a', 'c', 'd']), {'a': 'a', 'c': 'c', 'd': 'd'})
         self.assertEqual(self.cache.get_many(['a', 'b', 'e']), {'a': 'a', 'b': 'b'})
 
+    def test_get_many_works_with_empty_keys_array(self):
+        self.assertEqual(self.cache.get_many([]), {})
+
     def test_get_many_with_manual_integer_insertion(self):
         keys = ['a', 'b', 'c', 'd']
         for i, key in enumerate(keys):