False positive when assigning an empty dict to a union of dicts or Mappings

[hamdanal]

Bug Report

Like the title says.
I thought it might be because of dict variance but mapping union errors as well.

To Reproduce

from collections.abc import Mapping

d1: dict[str, str] | dict[int, int] = {}
d2: Mapping[str, str] | Mapping[int, int] = {}

reveal_type(d1)
reveal_type(d2)

Expected Behavior

No errors.

Actual Behavior

$ mypy t.py
t.py:3: error: Incompatible types in assignment (expression has type "dict[<nothing>, <nothing>]", variable has type "dict[str, str] | dict[int, int]")  [assignment]
t.py:4: error: Incompatible types in assignment (expression has type "dict[<nothing>, <nothing>]", variable has type "Mapping[str, str] | Mapping[int, int]")  [assignment]
t.py:6: note: Revealed type is "Union[builtins.dict[builtins.str, builtins.str], builtins.dict[builtins.int, builtins.int]]"
t.py:7: note: Revealed type is "Union[typing.Mapping[builtins.str, builtins.str], typing.Mapping[builtins.int, builtins.int]]"

Your Environment

• Mypy version used: mypy 1.5.1 (compiled: yes)
• Mypy command-line flags: N/A
• Mypy configuration options from mypy.ini (and other config files): N/A
• Python version used: 3.10

[ilevkivskyi]

A duplicate of #6463