code: @Nonnull
    @ReturnsMutableCopy
    public ICommonsList <String> cancelUploadedFiles (@Nullable final String... aFieldNames)
    {
      final ICommonsList <String> ret = new CommonsArrayList <> ();
      if (ArrayHelper.isNotEmpty (aFieldNames))
      {
        m_aRWLock.writeLocked ( () -> {
          for (final String sFieldName : aFieldNames)
          {
            final TemporaryUserDataObject aUDO = m_aMap.remove (sFieldName);
            if (aUDO != null)
            {
              _deleteUDO (aUDO);
              ret.add (sFieldName);
            }
          }
        });
      }
      return ret;
    }
docs: Remove all uploaded files and delete the underlying UDO objects. This is
  usually called, when the operation is cancelled without saving.
  
  @param aFieldNames
  The IDs to be removed and deleted.
  @return A non-<code>null</code> list with all field names that could be
  resolved and were removed.
  @see #confirmUploadedFiles(String...)