Bug Report

Consider a code checking whether all elements of a list are true. If so, it prints every element to the console with appended exclamation mark. If not, it should skip execution and print appropriate message

To Reproduce

example 1 - mypy returns failure

li = [None, "a"]

if not all(li):
    print("Not all elems of li are true")
else:
    for elem in li:
        print(elem + "!")

example 2 - mypy ok

li = ["a", "b"]

if not all(li):
    print("Not all elems of li are true")
else:
    for elem in li:
        print(elem + "!")

Expected Behavior
mypy should not report an error in line 7: print(elem + "!") - python cannot reach this code due to the condition: if not all(li):

Actual Behavior
example 1 fails:

main.py:7: error: Unsupported left operand type for + ("None")  [operator]
main.py:7: note: Left operand is of type "str | None"
Found 1 error in 1 file (checked 1 source file)

Your Environment

• Mypy version used: mypy 1.8.0, mypy master (from https://mypy-play.net)
• Mypy command-line flags: none, mypy-play was used
• Mypy configuration options from mypy.ini (and other config files): none
• Python version used: 3.11, 3.12