QGIS export composer as pdf in python

I have a QGIS project which contains a composer. Of course if I go into the GUI I can export it as a pdf etc. For my make script though I want to have this done via a python script. From reading online here is my attempt:

#!/usr/bin/env python

import sys
from qgis.gui import QgsMapCanvas, QgsLayerTreeMapCanvasBridge
from PyQt4.QtCore import QFileInfo

from PyQt4.QtXml import QDomDocument
from qgis.core import *

qgs = QgsApplication(sys.argv, True) 
QgsApplication.setPrefixPath("/usr", True) 

qgs.initQgis()

def make_pdf():
  canvas = QgsMapCanvas()

  bridge = QgsLayerTreeMapCanvasBridge(
      QgsProject.instance().layerTreeRoot(), canvas)
  bridge.setCanvasLayers()
  QgsProject.instance().read(QFileInfo('../board.qgs'))

  composition = QgsComposition(canvas.mapSettings())
  map_item = composition.getComposerItemById('board36x48')
  map_item.setMapCanvas(canvas)
  map_item.zoomToExtent(canvas.extent())
  composition.refreshItems()

  composition.exportAsPDF('generated/board.pdf')
  QgsProject.instance().clear()

make_pdf()

This fails, specifically:

i:./assets/generate_board 
QGraphicsScene::addItem: item has already been added to this scene
Traceback (most recent call last):
  File "./assets/generate_board", line 30, in 

    make_pdf()
  File "./assets/generate_board", line 24, in make_pdf
    map_item.setMapCanvas(canvas)
AttributeError: 'NoneType' object has no attribute 'setMapCanvas'

I based this off of Save Print/Map QGIS composer view as PNG/PDF using Python (without changing anything in visible layout)? but modified it to simplify as much as possible. It seems like I broke something in the process... I don't have this template file. I simple have a board.qgs project file with a composer board36x48. Any ideas?