If the_excerpt() is blank?

I am using the_content() and the_excerpt() on my index page. Its a resource site where we link to others. With the_content() (and more) we have our text and then we use the_excerpt() to quote the site we are linking to. The problem arises when we post our own articles. We have no need for the_excerpt() and need to not display it if we left it blank. However doing a simple if (the_excerpt()) doesn’t work since wordpress just uses content for it.

Is there another way to do this? Since I have the_excerpt() wrapped with blockquote, is there a way to wrap the whole thing in an if statement?