Rails Partial rendering results in a blank page? - ruby-on-rails

Question

I'm stuck with a bug at the moment which is puzzling me. I have a
layout containing some HTML and a partial (for the navigation) - there
is nothing else there other than the yield.
If the nav is included as a partial I get nothing returned to the
browser at all (blank page) but everything else appears normal
If I remove the partial the page works fine
If I put the nav code directly in the template it works fine
if I replace the nav code in the partial with a simple string, I get
a blank page again.
Does anyone have any ideas as to what the problem could be, or know how
I might debug it?

Answer 1

Found the issue, the partial was in the layouts folder, instead of the
relevant controller views folder.
However, Rails was throwing a ActionView::MissingTemplate Exception
which was only visible via the debugger which is probably a bug.

Answer 2

First off, check the log file to see if you're getting an error message somewhere. If that doesn't help follow these steps:
Make a copy of your template & partial, linked as the original
Test that they exhibit the problem
Start removing things from them until you have the simplest possible case that still exhibits the problem (your string in the partial test is a step in this direction)
If you don't figure it out in that process, come back and edit your question to include the code for the simplified case

Answer 3

I have had this error on a number of occasions. The problem has always been solved by changing something in the offending template or one of it's partials (in my latest case, I added a blank line into the source between a </div> and a <div>, which was in a partial invoked by the template; changing the template itself had no effect). The really odd thing is that the problem rarely occurs when I actually change a template, but usually when I change something related (e.g. edit an image displayed in the page or the CSS relating to the page). While the problem is often related to a partial, the entire page is blank, not just the portion provided by the partial.
BTW, restarting the web server (in this case Unicorn) does not fix the problem. Running Ruby 1.9.3, Rails 3.1.3. Using SASS and Unicorn.
UPDATE: Just determined that Rails is returning a 304-not modified, based upon the "If-none-match" header sent by my browser (which in turn was based upon the ETAG of the previous page). However, in the meantime, the browser cleared the window. So, presumably, something in what Rails sent caused the browser to clear the window.