Describe the bug

When i try to add a parameter node to activities on an activity diagram, sometimes it causes the editor to crash. I have tried gaphor on both linux and OS X and it is happening on both OSes. I have captured the error logs for the first time the crash happened and is linked below.

parameter-node-crash-report.txt

Now after the editor has crashed, the editor seemingly crashes every time i try to add a action to an activity diagram. This functioned properly before and the previous crash due to the parameter node seems to have caused this too. I have added 2 error reports which occured after that first crash due to the parameter node.

activity-node-crash-report-1.txt
activity-node-crash-report-2.txt

To Reproduce

Steps to reproduce the behavior:

1. Create a blank diagram.
2. Add an activity node to the diagram.
3. Add an action node to the diagram outside of the activity node
4. Add a parameter node to the activity node.

Expected behavior

gaphor does not crash when adding parameter nodes.

Screenshots

If applicable, add screenshots to help explain your problem.

OS

• Linux (Please put in notes the specific distro)
• macOS
• Windows

Version

Version of Gaphor: 2.19.1

Additional information

Linux distro: Ubuntu