code: @Nonnull
    public EChange registerMimeTypeContent (@Nonnull final MimeTypeContent aMimeTypeContent)
    {
      ValueEnforcer.notNull (aMimeTypeContent, "MimeTypeContent");
  
      return m_aRWLock.writeLocked ( () -> m_aMimeTypeContents.addObject (aMimeTypeContent));
    }
docs: Register a new MIME content type.
  
  @param aMimeTypeContent
  The content type to register. May not be <code>null</code>.
  @return {@link EChange#CHANGED} if the object was successfully registered.