class HexaPDF::Stream

def after_data_change

Makes sure that the stream data is either a String or a HexaPDF::StreamData object. 
def after_data_change
  super
  data.stream ||= ''.b
  unless data.stream.kind_of?(StreamData) || data.stream.kind_of?(String)
    raise ArgumentError, "Object of class #{data.stream.class} cannot be used as stream value"
  end
end