aasm.from_state is not always populated

[steamwings]

Describe the bug
aasm.from_state is empty for callbacks when the transition does not define from states. Not specifying from states is very useful when the state should be immediately reachable from any other state.

To Reproduce
Steps to reproduce the behavior:

Here's a small (untested) example that should get the idea across. The important thing is to include a transition with no from (transitions from any state) and a callback that will use aasm.from_state in response to that transition.

aasm do
  state :awake, initial: true
  state :tired
  # other states...
 
  after_all_transitions :log_status_change

  event :coffee do
    transitions to: :awake
  end

  event :party do
    transitions to: :tired
  end
end

def log_status_change
  puts "changing from #{aasm.from_state} to #{aasm.to_state} (event: #{aasm.current_event})"
end

Expected behavior
aasm.to_state is populated in all cases, but aasm.from_state is not populated for events like :coffee and :party in the above example.