title: Rails: HABTM - find all records with no association
body: <p>I have 2 models (Workout, Equipment) in a has and belongs to many relationship. If I use <code>Workout.find(:all, :joins =&gt; :equipment, :conditions =&gt; "equipment.id = 5")</code> it works, but if I use <code>Workout.find(:all, :joins =&gt; :equipment, :conditions =&gt; "equipment.id = null")</code> it doesn't return the records with no association. Any ideas?</p>