From a00fb21d37dc5d4486aba8302ab41cb54fe50f7c Mon Sep 17 00:00:00 2001
From: Kyle Banker <kylebanker@gmail.com>
Date: Mon, 12 Jul 2010 14:33:52 -0400
Subject: [PATCH] minor: better error message for DB#command

---
 lib/mongo/db.rb | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/lib/mongo/db.rb b/lib/mongo/db.rb
index dd24606..fc8de83 100644
--- a/lib/mongo/db.rb
+++ b/lib/mongo/db.rb
@@ -466,7 +466,9 @@ module Mongo
       result = Cursor.new(system_command_collection,
         :limit => -1, :selector => selector, :socket => sock).next_document
 
-      if result.nil? || (check_response && !ok?(result))
+      if result.nil?
+        raise OperationFailure, "Database command '#{selector.keys.first}' failed: returned null."
+      elsif (check_response && !ok?(result))
         raise OperationFailure, "Database command '#{selector.keys.first}' failed: #{result.inspect}"
       else
         result