Formatting a possibly nil value as hours and minutes

This might be a bit silly because there are like a thousand ways to do this, but I'm struggling to come up with one that I like. I feel like this should fit in one line, but I don't like re-using read_attribute(:length) lots and I don't like the below because it's not that clear.

# returns a human-readable string in the format Xh Ym
def length
  # length stored in seconds
  len = read_attribute(:length)
  "#{(len/60/60).floor}h #{len.modulo(60*60)/60}m" unless len.nil?
end

In one line

def length
  (len = read_attribute(:length)) && "#{(len/60/60).floor}h #{len.modulo(60*60)/60}m"
end

If len == nil return nil, if not - second operand

StackExchange Code Review Q#1855, answer score: 6