# Strange issue in Slicer 5.9 (revision 33881) that set qMRMLSubjectHierarchyComboBox to None

**URL:** <https://discourse.slicer.org/t/strange-issue-in-slicer-5-9-revision-33881-that-set-qmrmlsubjecthierarchycombobox-to-none/44215>\
**Category:** Development\
**Tags:** python\
**Created:** [August 27, 2025, 7:02am UTC](https://discourse.slicer.org/t/strange-issue-in-slicer-5-9-revision-33881-that-set-qmrmlsubjecthierarchycombobox-to-none/44215 "2025-08-27T07:02:24Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![chz31](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/chz31/32/77363_2.png) [@chz31](https://discourse.slicer.org/u/chz31)\
**Post date:** [August 27, 2025, 7:02am UTC](https://discourse.slicer.org/t/strange-issue-in-slicer-5-9-revision-33881-that-set-qmrmlsubjecthierarchycombobox-to-none/44215/1 "2025-08-27T07:02:24Z")

</div>

Hi,

I encountered a weird issue. I made a customized extension for surgical plate registration that runs well in Slicer 5.8.1 across platforms.

However, in the most recent Slicer 5.9 (revision 33881), whenever I ran a button linked to a simple [fiducial rigid registration function](https://github.com/chz31/SlicerOrbitSurgerySim/blob/9cb83b2d38affc637d219b909de1675f0f96a872/plateRegistration/plateRegistration.py#L661C2-L721C55) `onInitialRegistrationPushButton` (line 661), all the nodes in `qMRMLSubjectHierarchyComboBox` were set to None and I got ‘`NoneType`’ error since they are also connected to the parameter node.

There is no line in that function ([link to the script](https://github.com/chz31/SlicerOrbitSurgerySim/blob/9cb83b2d38affc637d219b909de1675f0f96a872/plateRegistration/plateRegistration.py#L661C2-L721C55)) that set up those comboBoxes to None. The only lines relevant to the combo boxes are (see above hyperlink to the full script):

```auto
self.ui.inputOrbitModelSelector.enabled = False
self.ui.orbitFiducialSelector.enabled = False
self.ui.plateModelSelector.enabled = False
self.ui.plateFiducialSelector.enabled = False

```

However, I don’t think these are relevant. Even if I commented them out, all those comboBoxes are still set to None.

I tested on Windows and Mac, and the issue persists. I will test it on Linux soon.

To reproduce, download the [repository](https://github.com/chz31/SlicerOrbitSurgerySim)and use Extension Wizard to load it to Slicer 5.9 (revision 33881). Switch to ‘plateRegistration’ module.

Download the sample data: [orbitSurgeySim\_sampleData/plateRegistrationSampleData.zip at main · chz31/orbitSurgeySim\_sampleData · GitHub](https://github.com/chz31/orbitSurgeySim_sampleData/blob/main/plateRegistrationSampleData.zip)

Drag the files into Slicer and populate the qMRMLSubjectHierarchyComboboxes, then click the ‘Initial Registration’ button.

 ![image](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/8/6/8644d7176c0a366293095926759eceac06b93d68.png)

 ![image](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/d/f/df5fdeabc0d01d64f382ded26f7932f763bdb537.png)

If it runs well, it should simply disable the qMRMLSubjectHiearchyComboBoxes without setting it to None:

 ![image](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/4/4/44afd9d09ffa7c1ed194cc9c970a7e02c485c93c.png)

Thank you!

---

<div class="post-metadata">

**Author:** ![chz31](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/chz31/32/77363_2.png) [@chz31](https://discourse.slicer.org/u/chz31)\
**Post date:** [August 27, 2025, 8:42pm UTC](https://discourse.slicer.org/t/strange-issue-in-slicer-5-9-revision-33881-that-set-qmrmlsubjecthierarchycombobox-to-none/44215/2 "2025-08-27T20:42:35Z")

</div>

I found a version of Slicer 5.9.0 in my Linux computer built in 07-25. Interestingly, there was no such issue of automatically setting the qMRMLSubjectHierarchyComboBox to None.