Optional types not being narrowed after a logical-and followed by a test of one of the operands

(Sorry if the title is overly specific)

• Are you reporting a bug, or opening a feature request?

Bug

• Please insert below the code you are checking with mypy,
  or a mock-up repro if the source is private. We would appreciate
  if you try to simplify your case to a minimal repro.

from typing import Optional

def get_org_id(org_name: str) -> str:
    return 'some_org_id'

def create(org_name: Optional[str], org_id: Optional[str]):
    if not org_name and not org_id:
        raise ValueError('No org specified')
    if not org_id:
        org_id = get_org_id(org_name)

• What is the actual behavior/output?

The inferred type of org_name at the last line is Optional[str] (technically Union[builtins.str, None]).

• What is the behavior/output you expect?

The type should be narrowed to str.

• What are the versions of mypy and Python you are using?
  Do you see the same issue after installing mypy from Git master?

Python 3.7.3
mypy: 0.701

• What are the mypy flags you are using? (For example --strict-optional)

No flags

issue にある最小限の Python 再現コードから始め、論理 AND 条件の後で org_name に推論される型を確認します。org_name と org_id の型の絞り込みの動作を追跡し、このケースのカバレッジを追加します。完了条件は、関連するオプショナル型の絞り込みを壊すことなく、get_org_id の呼び出し時に org_name が str として推論されることです。