S0006: allow empty emergencystate when status is False

[emiltin]

the 1.1 spec is not clear about the value of emergencystate when status=False.

Current implementations send an empty string. I suggest we allow this for 1.1 and older. in upcoming version of the sxl, this should be clarified

[emiltin]

allowing empty string if status=False can be done in json schema, but not with our sxl yaml source. instead we can allow emergencystate=0, but that means implementations that send null will fail tests.

[otterdahl]

If we allow null instead of empty strings, then we should update the core spec as well.

Section 4.4:

Empty values are sent as ""

[emiltin]

Benefits would be:

• there can be a difference between an empty string and null
• null is a separate type in json and json schema, making it easy to define and validate.

Drawbacks:

• implementations cannot any longer assume that n in a status response is always a string. They need to handle nulls.

The simplest we can do now is probably to allow only integers (as string) and define that n=0 means to route active. In upcoming versions of core we can then consider the use of nulls and other native types throughout the spec.

[emiltin]

closing, as #70 allows emergencyState=0