Raise error if passing empty array to mget

lib/mock_redis/string_methods.rb

@@ -154,9 +154,10 @@ def incrbyfloat(key, n)
     end
 
     def mget(*keys)
+      keys.flatten!
+
       assert_has_args(keys, 'mget')
 
-      keys.flatten!
       keys.map do |key|
         get(key) if stringy?(key)
       end

spec/commands/mget_spec.rb

@@ -49,5 +49,11 @@
         @redises.mget
       end.should raise_error(Redis::CommandError)
     end
+
+    it 'raises an error if you pass it empty array' do
+      lambda do
+        @redises.mget([])
+      end.should raise_error(Redis::CommandError)
+    end
   end
 end