OLAT-6362 : prevent archiving empty folders when archiving Task bb

--HG--
branch : uzhFixes711

olat3/webapp/WEB-INF/src/org/olat/course/nodes/TACourseNode.java

@@ -840,10 +840,21 @@ public class TACourseNode extends GenericCourseNode implements AssessableCourseN
 			}
 			// copy dropboxes to tmp dir
 			if (dropboxDir.exists()) {
-				FileUtils.copyDirContentsToDir(dropboxDir, new File(tmpDirPath + "/dropboxes"),false, "archive task course node dropboxes" );
-				fileList.add("dropboxes");
-				//dropboxes exists, so there is something to archive
-				dataFound = true;
+			//OLAT-6362 archive only dropboxes of users that handed in at least one file -> prevent empty folders in archive
+				File[] dropBoxContent = dropboxDir.listFiles();
+				boolean validDropboxesfound = false;
+				for (File file : dropBoxContent) {
+					if(file.isDirectory() && !FileUtils.isDirectoryEmpty(file)){
+						validDropboxesfound = true;
+						FileUtils.copyDirContentsToDir(file, new File(tmpDirPath + "/dropboxes/"+file.getName()), false, "archive task course node dropboxes "+file.getName());
+					}
+				}
+				
+				if(validDropboxesfound){
+					// dropboxes exists and at least one is not empty, so there is something to archive
+					dataFound = true;
+					fileList.add("dropboxes");
+				}
 			}
 			// copy only the choosen task to user taskfolder, loop over all users
 			String taskfolderPath = FolderConfig.getCanonicalRoot() + TACourseNode.getTaskFolderPathRelToFolderRoot(course.getCourseEnvironment(),this);