eclipse Source folder name is empty.

This error message usually appears when you are trying to create a new Java source folder in Eclipse, but you have not given it a name. To resolve this issue, follow these steps:

1. Right-click on your project in the Package Explorer view.
2. Select New -> Source Folder.
3. In the New Source Folder dialog box, enter a name for your source folder in the Folder name field.
4. Click Finish to create the new source folder.

If you already have a source folder in your project and you are seeing this error message, it may be because the folder has been deleted or moved. In this case, you will need to update your project's build path to point to the correct source folder. To do this, right-click on your project and select Build Path -> Configure Build Path. In the Build Path dialog box, select the Source tab and make sure the correct source folder is listed. If it is not, click Add Folder and select the correct folder from the list.