Starting integrated server. opened minecraft and says play offline. click that and try to open a world. it crashes everytime

Put the summary of the bug you're having here

What I expected to happen was...:
Describe what you thought should happen here
minecraft would open and work properly

What actually happened was...:
Describe what happened here
update notes don't appear, can only play offline, worlds crash while loading
Steps to Reproduce:
1. open minecraft
2. click play offline
3. open world
4. crashes