Traceback (most recent call last):
  File "test_rgb2ycbcr.py", line 96, in <module>
    testbench()
  File "test_rgb2ycbcr.py", line 93, in testbench
    assert instance.verify_convert() == 0
  File "/usr/local/lib/python2.7/dist-packages/myhdl-1.0.dev0-py2.7.egg/myhdl/_block.py", line 218, in verify_convert
    return myhdl.conversion.verify(self)
  File "/usr/local/lib/python2.7/dist-packages/myhdl-1.0.dev0-py2.7.egg/myhdl/conversion/_verify.py", line 144, in __call__
    inst = func.convert(hdl='Verilog')
  File "/usr/local/lib/python2.7/dist-packages/myhdl-1.0.dev0-py2.7.egg/myhdl/_block.py", line 256, in convert
    return converter(self)
  File "/usr/local/lib/python2.7/dist-packages/myhdl-1.0.dev0-py2.7.egg/myhdl/conversion/_toVerilog.py", line 175, in __call__
    genlist = _analyzeGens(arglist, h.absnames)
  File "/usr/local/lib/python2.7/dist-packages/myhdl-1.0.dev0-py2.7.egg/myhdl/conversion/_analyze.py", line 174, in _analyzeGens
    tree.symdict = f.f_globals.copy()
AttributeError: 'NoneType' object has no attribute 'f_globals'