NoneType not being properly filtered out after checking if obj is None · Issue #8851

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I am reporting what I believe is a bug, where mypy.types.NoneType doesn't work, where "None" does, when filtering for None using a check similar to obj is None .

Also, reveal_type doesn't work in is None checks with NoneType being used.

What do I expect? I expect NoneType to equal "None" . Please see the below code samples to better explain.

Repro With Potential NoneType Bug

from typing import TypeVar
from mypy.types import NoneType
FloatOrNone = TypeVar("FloatOrNone", float, NoneType)
def test_none_type(val: FloatOrNone) -> FloatOrNone:
    if val is None:
        reveal_type(val)
        # Doesn't even get checked
        return val
    reveal_type(val)
    # Normally I would do something with a `float` value here
    # Revealed type is 'mypy.types.NoneType*'
    # Revealed type is 'builtins.float*'
    return val
1.0 > test_none_type(None)
1.0 > test_none_type(0.5)

And the mypy output:

some_path/some_file.py: note: In function "test_none_type":
some_path/some_file.py:20: note: Revealed type is 'builtins.float*'
some_path/some_file.py:20: note: Revealed type is 'mypy.types.NoneType*'
some_path/some_file.py: note: At top level:
some_path/some_file.py:28: error: Value of type variable "FloatOrNone" of "test_none_type" cannot be "None"  [type-var]
some_path/some_file.py:28: error: Unsupported operand types for > ("float" and "None")  [operator]
You can see:
The check for val is None didn't properly filter for None.
reveal_type didn't work in the is None check
There is a mistaken type-var error in the 2nd to last line
Repro with "None" Success
from typing import TypeVar
FloatOrNone = TypeVar("FloatOrNone", float, "None")
def test_none_type(val: FloatOrNone) -> FloatOrNone:
    if val is None:
        reveal_type(val)
        # Revealed type is 'None'
        return val
    reveal_type(val)
    # Normally I would do something with a `float` value here
    # Revealed type is 'builtins.float*'
    return val
1.0 > test_none_type(None)
1.0 > test_none_type(0.5)
And the mypy output:
some_path/some_file.py: note: In function "test_none_type":
some_path/some_file.py: note: Revealed type is 'None'
some_path/some_file.py: note: Revealed type is 'builtins.float*'
some_path/some_file.py: note: At top level:
some_path/some_file.py: error: Unsupported operand types for > ("float" and "None")  [operator]
Works as expected.
Versions
mypy==0.770
python==3.6.5
          No there isn't documentation from what I had seen, I just came across it once in the source.  Based on its docstring, I thought it was useful (turns out I was wrong).
Before this ticket disappears for all time, I would like to sneak in one question: is there a difference between "None" and None when entered as a value restriction in TypeVar?
Why do I ask?  My IDE (PyCharm, PE version 2020.1) complains about using a raw None, saying Expected type 'Union[type, str]', got 'None' instead.  If there's no difference between None and "None" w.r.t. mypy, I will continue using "None".