Detect content in minibuffer

[Miguel Guedes]

I'm using the following to query the size of the buffer associated with 
the minibuffer but it always returns 0 even when there is a message 
currently being displayed in the echo area (say, documentation by eldoc 
or anything else).  The aim is to not echo anything when there's 
currently content in the echo area.

I've tried:

(with-current-buffer (window-buffer (minibuffer-window))
  (unless (> 0 (buffer-size))
    .
    :
    .

and [0],

(with-current-buffer (get-buffer " *Echo Area 0*")
  (unless (> 0 (buffer-size))
    .
    :
    .

What's wrong with my approach?

--
[0] Found excerpt referring to the echo area as "*Echo Area 0*" at 
http://www.emacswiki.org/emacs/EchoArea