Check for missing keywords

Has anyone come up with a clever control process to check for missing keywords? (Something more efficient than going through each gallery one by one?) As a newbie who is just beginning to load images, I'm planning to load my keywords manually via the caption/keyword tool. The keyword cloud is going to be important for me, and I want every image to be represented there. But I just know I'll occasionally have a senior moment and forget one. I don't suppose there's something like a search string that represents null? Any other ideas?

Thanks!