`AsDiscreted` bug when `threshold=0.0`

[yiheng-wang-nv]

Reproduce the bug:

from monai.transforms import AsDiscreted
a = AsDiscreted(keys="pred", threshold=0.0)

[Nic-Ma]

Hi @yiheng-wang-nv ,

Thanks for your bug report, let me fix it now.

[yiheng-wang-nv]

I think the PR in #3388 does not solve the issue, and a threshold=0.0 test case does not added in the PR.
As you can see:

[yiheng-wang-nv]

I think I've found the error place:

MONAI/monai/transforms/post/array.py

Line 246 in 839f7ef

threshold = threshold or self.threshold

@Nic-Ma , this line is wrong since 0.0 or None is None.
In addition, parameters in __call__ of AsDiscrete are not covered in test_as_discrete.py, thus the test function does not find this issue, I think we may need more test cases.

[Nic-Ma]

Hi @yiheng-wang-nv ,

Thanks for your test, let me have a try and investigate it ASAP.

[Nic-Ma]

Hi @yiheng-wang-nv ,

I submitted PR #3393 to fix it and added more unit tests to cover the threshold=0.0 case.
The call() function of array transform is already covered by the dict transform, because:
https://github.com/Project-MONAI/MONAI/blob/dev/monai/transforms/post/dictionary.py#L204
Could you please help review it?

Thanks in advance.