I am not sure if we can accept pull request targeting the main branch. There is a limitation due to the current license hold in the main branch that has been included after the 4.2.2 release and just before the original mxgraph EOL, see jgraph#505
I addition, we may remove the java support from this repo, see #32 (comment)

I understand. Just a question on the license, I see that the latest license is also in the development branch, does that mean the limitation you mentioned also applies to the development branch?

I guess that for now, yes we have the license limitation.
I didn't have time to open a discussion to talk with the other contributors about this topic, but this is something we have to clarify as soon as as possible.

Wow, that license change looks bad. It would be great if it is solvable, otherwise we might never be able to change to this project and might need to downgrade our used mxgraph version

The license change has been introduced after the mxgraph 4.2.2 release and soon before the original implementation reach end of life.
All code released prior the license change is still covered by the default/regular Apache-2.0 license without the modified clause 4e of Apache 2 license (with restricts works targetting Atlassian's Jira or Confluence products). And I guess that we don't want to keep this restriction with the initiative in progress in the new repository.