An error occurred while running the workspace with a javaplugin

I wanted to create a java plugin (I just added a new ModElement for testing) and when I wanted to open a workspace with this plugin, it gave me this error and I don't understand why.

2024-03-12-22:37:26 [AWT-EventQueue-0/INFO] [MCreator] Opening MCreator workspace: api_test
2024-03-12-22:37:27 [pool-4-thread-1/INFO] [GA4] Tracked event: new_workspace, context: forge-1.20.1
2024-03-12-22:37:27 [Image Fetcher 0/ERROR] [STDERR] Uncaught error fetching image:
2024-03-12-22:37:27 [Image Fetcher 0/ERROR] [STDERR] java.lang.NullPointerException: Cannot invoke "java.net.URL.openConnection()" because "this.url" is null
2024-03-12-22:37:27 [Image Fetcher 0/ERROR] [STDERR] at java.desktop/sun.awt.image.URLImageSource.getConnection(URLImageSource.java:103)
2024-03-12-22:37:27 [Image Fetcher 0/ERROR] [STDERR] at java.desktop/sun.awt.image.URLImageSource.getDecoder(URLImageSource.java:113)
2024-03-12-22:37:27 [Image Fetcher 0/ERROR] [STDERR] at java.desktop/sun.awt.image.InputStreamImageSource.doFetch(InputStreamImageSource.java:264)
2024-03-12-22:37:27 [Image Fetcher 0/ERROR] [STDERR] at java.desktop/sun.awt.image.ImageFetcher.fetchloop(ImageFetcher.java:212)
2024-03-12-22:37:27 [Image Fetcher 0/ERROR] [STDERR] at java.desktop/sun.awt.image.ImageFetcher.run(ImageFetcher.java:176)

Because I didn't know much about javaplugin, I put another javaplugin (which works properly) as a template.