Program: 170313
Project: 170313
Buggy source:
public void skinLibraryCommand(EntityPlayerMP player,SkinLibraryCommand command,LibraryFile file,boolean publicList){
  if (!publicList) {
  }
switch (command) {
case DELETE:
    if (!publicList) {
      File dir=new File(SkinIOUtils.getSkinLibraryDirectory(),file.filePath);
      if (file.isDirectory()) {
        dir=new File(dir,file.fileName + "String_Node_Str");
      }
 else {
        dir=new File(dir,file.fileName + SkinIOUtils.SKIN_FILE_EXTENSION);
      }
      if (dir.isDirectory() == file.isDirectory()) {
        if (dir.exists()) {
          if (file.isDirectory()) {
            try {
              FileUtils.deleteDirectory(dir);
              libraryManager.reloadLibrary();
            }
 catch (            IOException e) {
              e.printStackTrace();
            }
          }
 else {
            CommonSkinCache.INSTANCE.clearFileNameIdLink(file);
            dir.delete();
            libraryManager.reloadLibrary();
          }
        }
      }
    }
 else {
      ModLogger.log("String_Node_Str");
    }
  break;
case NEW_FOLDER:
if (!publicList) {
  File dir=new File(SkinIOUtils.getSkinLibraryDirectory(),file.filePath);
  ModLogger.log(dir.getAbsolutePath());
  dir=new File(dir,file.fileName);
  if (!dir.exists()) {
    dir.mkdir();
  }
  libraryManager.reloadLibrary();
  ModLogger.log(String.format("String_Node_Str",file.fileName,file.filePath));
  ModLogger.log("String_Node_Str" + dir.getAbsolutePath());
}
 else {
  ModLogger.log("String_Node_Str");
}
break;
}
}

Fixed version (ground truth):
public void skinLibraryCommand(EntityPlayerMP player,SkinLibraryCommand command,LibraryFile file,boolean publicList){
  if (!publicList) {
  }
switch (command) {
case DELETE:
    if (!publicList) {
      File dir=new File(SkinIOUtils.getSkinLibraryDirectory(),file.filePath);
      if (file.isDirectory()) {
        dir=new File(dir,file.fileName + "String_Node_Str");
      }
 else {
        dir=new File(dir,file.fileName + SkinIOUtils.SKIN_FILE_EXTENSION);
      }
      if (dir.isDirectory() == file.isDirectory()) {
        if (dir.exists()) {
          if (file.isDirectory()) {
            try {
              FileUtils.deleteDirectory(dir);
              libraryManager.reloadLibrary();
            }
 catch (            IOException e) {
              e.printStackTrace();
            }
          }
 else {
            clearFiles.add(file);
            ModLogger.log("String_Node_Str" + dir.getAbsolutePath());
            dir.delete();
            libraryManager.removeFileFromListType(file,LibraryFileType.SERVER_PRIVATE,player);
            libraryManager.reloadLibrary(this);
          }
        }
      }
    }
 else {
      ModLogger.log("String_Node_Str");
    }
  break;
case NEW_FOLDER:
if (!publicList) {
  File dir=new File(SkinIOUtils.getSkinLibraryDirectory(),file.filePath);
  ModLogger.log(dir.getAbsolutePath());
  dir=new File(dir,file.fileName);
  if (!dir.exists()) {
    dir.mkdir();
  }
  libraryManager.reloadLibrary();
  ModLogger.log(String.format("String_Node_Str",file.fileName,file.filePath));
  ModLogger.log("String_Node_Str" + dir.getAbsolutePath());
}
 else {
  ModLogger.log("String_Node_Str");
}
break;
}
}