AttributeError: 'NoneType' object has no attribute 'split'

scons: Reading SConscript files ...
AttributeError: 'NoneType' object has no attribute 'split':
  File "/home/rtbkit/platform-deps/mongo-cxx-driver/SConstruct", line 75:
    for x in os.getenv("/home/rtbkit/local/lib:").split(":")