Reproduction steps:
1. Open the attached project "GenerateBug"
2. Open Unit Options Wizard (Tools > Bolt > Unit Options Window)
3. Scroll down and click "Next"
4. Scroll down and click "Generate"

Expected result: No errors are thrown
Actual result: "NullReferenceException" error is thrown:
NullReferenceException: Object reference not set to an instance of an object
Ludiq.Icons.GetScriptTypeIcon (System.String scriptName) (at <af5e15b3589540ac94baeb6e74576eac>:0)
Ludiq.Icons.GetCustomTypeIcon (System.Type type, System.Boolean inherit) (at <af5e15b3589540ac94baeb6e74576eac>:0)
Ludiq.Icons.Type (System.Type type) (at <af5e15b3589540ac94baeb6e74576eac>:0)
Ludiq.Icons.Icon (System.Type type) (at <af5e15b3589540ac94baeb6e74576eac>:0)

Reproducible with: 1.4.15 (2021.2.0a19, 2021.2.1f1, 2021.2.3f1, 2022.1.0a16)
Not reproducible with: 1.4.15 (2021.1.28f1, 2021.2.0a18, 2021.2.0f1)
Could not test with: 1.4.15 (2019.4.33f1, Assembly 'Assets/Ludiq/Assemblies/Bolt.Flow.Editor.dll' will not be loaded due to errors: Reference has errors 'Ludiq.Core.Editor', 2020.3.23f1, An infinite import loop has been detected. The following Assets were imported multiple times, but no changes to them have been detected. Please check if any custom code is trying to import them:
Packages/com.unity.timeline/Editor/StyleSheets/Images/DarkSkin/TimelineMarkerItemSelected.png(modified date 2021-08-05T19:43:49Z)
Packages/com.unity.2d.animation/Editor/Assets/Icons/Dark/d_Sprite Resolver@8x.png(modified date 2021-10-05T14:38:08Z))

Notes:
- Sometimes the error is shown after about 1-2 minutes after clicking the "Generate" button