Recent issue has been introduced. Inside composite components when concatenating a string to a Private Variable that is blank, the private variable concatenates 'null' and then the additional string. The same issue does not occur with page variables etc - it seems to be only private variables inside composite components.
For example, app id 387452, page 1, the composite component custom-12d3ab34-b468-480e-871d-68fbf703e66f has a text box bound to the private variable (BlankValue), and a button that sets the private variable to privateVars.BlankValue+"a". This results in 'nulla' being set in the private variable and then being displayed to the user. This happens whether or not I set BlankValue to "" on component mount.
We discovered this issue on a much larger calculator composite component that we use and the bug has rendered the component useless.