I wouldn't want Joshua to eat his shoe, but....
What we're really talking about isn't so much a "dead spot" (although that's how the issue presents itself to players), but rather the sympathetic frequency of the bass. When a particular note matches the sympathetic frequency of the bass itself, the bass will absorb the energy of the string. The result is that the note will not ring as long or clear, and you'll feel greater vibration in the neck. Quite a number of factors will affect the sympathetic frequency of the bass - scale, types of wood used, mass, construction etc. - but in my experience this node usually shows up between the Bb and D (3rd to 7th frets on G string, 8th to 12th fret on D string). C to D seems more common for Fender style instruments, while Rickenbackers usually exhibit this a bit lower in the Bb to C range. I don't dispute that this may not be very noticeable on certain basses, but if I can't find the sympathetic frequency on a bass, I'll eat my touque.
P.S. My 4002 sympathetically vibrates at C (5th fret on G string).