Allow sending cache_dir=null in PATCH request-body

[tcompa]

In user's settings, we should also enable the possibility of setting cache_dir=null. Right now, if I try to set it to an empty string then the webclient sets cache_dir="" in the request body, which is then rejected from the backend.

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This is a specific case, but it most likely applies to several other forms. Let's find a solution which would also work for all of them.

[zonia3000]

We already have a function nullifyEmptyStrings that we use in similar cases. In most of the cases we are using stripNullAndEmptyObjectsAndArrays, so the empty string are removed from the payload.

However, in this particular case if I send null to the endpoint I receive another validation error:

{"detail":[{"loc":["body","cache_dir"],"msg":"command=None is not a string.","type":"value_error"}]}

Is this expected?

[tcompa]

However, in this particular case if I send null to the endpoint I receive another validation error:
...
{"detail":[{"loc":["body","cache_dir"],"msg":"command=None is not a string.","type":"value_error"}]}
Is this expected?

No, it's not expected - and it's to be fixed on the backend side. Thanks!