code: @Nullable
    public TemporaryUserDataObject getUploadedFile (@Nullable final String sFieldName)
    {
      if (StringHelper.hasNoText (sFieldName))
        return null;
  
      return m_aRWLock.readLocked ( () -> m_aMap.get (sFieldName));
    }
docs: Get the user data object matching the specified field name.
  
  @param sFieldName
  The ID to be searched. May be <code>null</code>.
  @return <code>null</code> if the passed field name could not be resolved.