you may disable the error reporting in Joomla global config till the new update is ready to fix this issue, I have already fixed it here
I have fixed this and updated the installer, you may download the installer again and install it over yours
The warning is triggered by a minor issue in the update.
Temporarily disable error reporting in the Joomla global configuration. Then, download and install the updated CF installer over the existing installation to permanently fix it.
you may disable the error reporting in Joomla global config till the new update is ready to fix this issue, I have already fixed it here
I have fixed this and updated the installer, you may download the installer again and install it over yours