Referencing invalid package names causes a compiler crash

[janicedatawire]

I changed the name of a package and missed a reference to the old name in the code. When I tried to compile the file, I got the following compiler crash:

$ quark --python ~/quark-examples/python examples/list.q
Traceback (most recent call last):
  File "/Users/janicekarin/virtualenv/bin/quark", line 9, in <module>
    load_entry_point('datawire-quark==0.1.0', 'console_scripts', 'quark')()
  File "/Users/janicekarin/quark/quark/compiler.py", line 566, in main
    exit(_main(docopt(main.__doc__)))
  File "/Users/janicekarin/quark/quark/compiler.py", line 542, in _main
    c.compile()
  File "/Users/janicekarin/quark/quark/compiler.py", line 497, in compile
    self.root.traverse(use)
  File "/Users/janicekarin/quark/quark/ast.py", line 93, in traverse
    c.traverse(visitor, *args, **kwargs)
  File "/Users/janicekarin/quark/quark/ast.py", line 93, in traverse
    c.traverse(visitor, *args, **kwargs)
  File "/Users/janicekarin/quark/quark/ast.py", line 93, in traverse
    c.traverse(visitor, *args, **kwargs)
  File "/Users/janicekarin/quark/quark/ast.py", line 93, in traverse
    c.traverse(visitor, *args, **kwargs)
  File "/Users/janicekarin/quark/quark/ast.py", line 93, in traverse
    c.traverse(visitor, *args, **kwargs)
  File "/Users/janicekarin/quark/quark/ast.py", line 93, in traverse
    c.traverse(visitor, *args, **kwargs)
  File "/Users/janicekarin/quark/quark/ast.py", line 94, in traverse
    leave(self, *args, **kwargs)
  File "/Users/janicekarin/quark/quark/compiler.py", line 233, in leave_Type
    if n.text in type.env:
AttributeError: 'NoneType' object has no attribute 'env'