Constructor returned NULL on making ghost pad

gistfile1.txt

GStreamer 1.0.0
<Pad object at 0x2b73230 (GstPad at 0x2bc60d0)>

(main.py:4385): GStreamer-CRITICAL **: gst_ghost_pad_new: assertion `!gst_pad_is_linked (target)' failed
Traceback (most recent call last):
  File "main.py", line 46, in <module>
    Main().run()
  File "main.py", line 21, in __init__
    self.station = station.Station()
  File "/home/lsimons/open-playout/station.py", line 19, in __init__
    self.cam1 = camera.Camera('cam1')
  File "/home/lsimons/open-playout/camera.py", line 27, in __init__
    ghost_pad = Gst.GhostPad.new("src",pad)
  File "/usr/lib/python2.7/dist-packages/gi/types.py", line 72, in constructor
    return info.invoke(cls, *args, **kwargs)
TypeError: constructor returned NULL
[1]+  Done                    clear
lsimons@bestever:~/open-playout$