Gradual default attributes breaks default constructors

[bartv]

fail.cf:

entity Server:
    string a="a"
    string b
end

typedef Server2 as Server(b="b")

Server2()

$ inmanta -vvv compile -f fail.cf -X
INFO     Creating new virtual environment in ./.env
DEBUG    Starting compile
INFO     verifying project
Traceback (most recent call last):
  File "/home/bart/workspace/inmanta/src/inmanta/app.py", line 471, in app
    options.func(options)
  File "/home/bart/workspace/inmanta/src/inmanta/app.py", line 154, in compile_project
    result = do_compile()
  File "/home/bart/workspace/inmanta/src/inmanta/compiler/__init__.py", line 45, in do_compile
    success = sched.run(compiler, statements, blocks)
  File "/home/bart/workspace/inmanta/src/inmanta/execute/scheduler.py", line 230, in run
    block.context.emit(queue.for_tracker(ModuleTracker(block)))
  File "/home/bart/workspace/inmanta/src/inmanta/execute/runtime.py", line 698, in emit
    self.block.emit(self, queue)
  File "/home/bart/workspace/inmanta/src/inmanta/ast/blocks.py", line 74, in emit
    s.emit(resolver, queue)
  File "/home/bart/workspace/inmanta/src/inmanta/ast/statements/__init__.py", line 91, in emit
    reqs = self.requires_emit(resolver, queue)
  File "/home/bart/workspace/inmanta/src/inmanta/ast/statements/generator.py", line 260, in requires_emit
    default_wrapper_type = {name: expr for name, expr in self.type.get_default_values().items()
AttributeError: 'Default' object has no attribute 'get_default_values'