Feat/support null values in data flag

[reubenmiller]

Add support for null values in the data flag.

null values are commonly used when updating managed objects to delete fragments. Previously the data flag was interpreting null as a string.

Example

Remove property from a managed object

Cumulocity support deletion of root fragment by sending an update to the managed object with the root fragment set to null.

c8y devices update --id 12345 --data "myFragment=null" --dry

Body

{
    "myFragment": null
}

If you want to remove the fragment from all managed objects containing this fragment then you can use it in a pipeline

c8y inventory find --query "has(myFragment)" --includeAll | c8y devices update --data "myFragment=null"