What PsychoPy version is used when no version is selected in properties?

Within the builder, you can change the version of PsychoPy by going to “properties” and then changing the “Use PsychoPy version” box to a specific version. However, by default, no version is selected here. If one opens the drop down menu for this setting, there is a check mark by a blank option, seemingly indicating that no version has been selected.

What version of PsychoPy is used when no version has been selected in properties as described above (i.e., when the “Use PsychoPy version” box in properties is set to blank)?