console.log(session.state) 
// { userName: 'God', colour: 'Green' }

async (input) => {
  ai.currentSession().updateState({ 
    colour: input.colour,
  });
  return `colour updated to ${input.colour}`;
}

console.log(session.state)
// { colour: 'Green' }  // userName was cleared

async (input) => {
  ai.currentSession().updateState({
    ...ai.currentSession().state,
    userName: input.userName,
  });
}