Reproduction steps:
1. Open the attached "EmptyFieldFallback.zip" project
2. Open the "SampleScene" Scene
3. In the Hierarchy, select the "Test" GameObject
4. In the Inspector, click on the "Num" property field
5. Delete the number inside
6. Press Enter or click outside the field

Expected result: "Num" property is set to 0. An empty number field is considered zero when pressing Enter or clicking outside the field but not when pressing Escape
Actual result: "Num" property returns to the deleted number. An empty field always fallbacks to the last value as if the Escape key is pressed

Reproducible with: 2021.2.0a10, 2021.2.0b3, 2022.1.0a2
Not reproducible with: 2018.4.36f1, 2019.4.29f1, 2020.3.14f1, 2021.1.15f1, 2021.2.0a9