mypy does not warn about incorrect default value in dict.get in some case

It seems that mypy should actually warn about the assignment of the set in the following code:

from typing import Dict, Any

params: Dict[str, Any] = {}
a: Dict[str, Any] = params.get("abc", set())
reveal_type(a)

mypy does not warn about the incorrect assignment of Set to a but correctly reveals that the type of a is Dict[str, Any]. Sadly the use of Any in this case is common as these dicts represent complex configuration files.

Tested with the current git master version.

Start with the minimal Python example in the issue and run mypy to confirm that the incompatible set() default is not reported for the Dict[str, Any] assignment. Trace the type-checking behavior for dict.get and Any, then add coverage showing that this case produces a warning while the revealed type remains appropriate.