As part of MDL-84107, removing mlbackend_php required the disabling of Analytics on new installs. This was because we replacemed it with mlbackend_python and the default processor, and it could not be assumed that admins had configured it correctly.

If we ignore the state of mlbackend_python, there will be exceptions, halting the use of Analytics until it is configured correctly. Even choosing the predictions processor as mlbackend_python will trigger those exceptions as it does checks before you can select it. You can see this selection at Site admin -> Analytics -> Analytics settings (predictionsprocessor).

We need to find a way to overcome this. There are a couple things to consider:

1. Should we have a way to select a processor provider without the checks that cause the exceptions? If you merely select 'Python machine learning backend', or if it is already selected and you press 'Save changes', you will notice it performs the checks and throws the exceptions if you do no have python configured.
2. Can we enable Analytics and have a 'null' predictions processor? This would require some rewiring. Models that don't specify a processor will use the default, and that default is represented as a constant DEFAULT_MLBACKEND