code: @Nonnull
    public EChange unregisterMimeTypeContent (@Nullable final MimeTypeContent aMimeTypeContent)
    {
      if (aMimeTypeContent == null)
        return EChange.UNCHANGED;
  
      return m_aRWLock.writeLocked ( () -> m_aMimeTypeContents.removeObject (aMimeTypeContent));
    }
docs: Unregister an existing MIME content type.
  
  @param aMimeTypeContent
  The content type to unregister. May not be <code>null</code>.
  @return {@link EChange#CHANGED} if the object was successfully
  unregistered.