How to deal with null/None values

[PeteCoward]

Currently a python None passed into the js options as attribute_value=null, and the code currently assumes this means there the object target cannot be deleted.
There is no way to set the attribute value to None, only to an empty string.
We display 'empty' when the value is None, or an empty string.

We may want to:

• have a visible distinction between empytish values 1. no value 2. value None 3. empty string
• allow deletion of emptyish values
• allow setting values to None ( not empty string