code: @Nonnull
    public String getContentAsBase64EncodedString ()
    {
      // Add Base64 encoded String
      final byte [] aEncoded = Base64.encodeBytesToBytes (m_aContent);
      // Print the string in the specified charset
      return new String (aEncoded, m_aCharset);
    }
docs: Get the content as a Base64 encoded {@link String} in the {@link Charset}
  specified by {@link #getCharset()}. The encoding is applied independent of
  the {@link #isBase64Encoded()} state.
  
  @return Never <code>null</code>.