PyObject doesn't work with None default #305
Description
Bug
import pydantic
class Foo(pydantic.BaseModel):
x: pydantic.PyObject = None
Foo()~/code/pydantic/pydantic/utils.py in import_string(dotted_path)
102 """
103 try:
--> 104 module_path, class_name = dotted_path.strip(' ').rsplit('.', 1)
105 except ValueError as e:
106 raise ImportError(f'"{dotted_path}" doesn\'t look like a module path') from e
AttributeError: 'NoneType' object has no attribute 'strip'