Oops, something I did in my hack won't work in all TOSCA parsers. (If tails in Puccini!) Here is a fixed version. The issue that the bare word "null" is interpreted in YAML as null. The following will work.
By the way, does your TOSCA parser support the "null" type? ;) It's a bit hidden away in the spec, but it is there. We should probably add a note about having to add quotes around "null" when it is used as a type.
data_types:
 Any:
  description: >-
ÂÂÂÂÂ Only one of the properties should be set!
  properties:
   boolean:
    type: boolean
    required: false
   integer:
    type: integer
    required: false
   float:
    type: float
    required: false
   string:
    type: string
    required: false
   list:
    type: list
    entry_schema: Any
    required: false
   map:
    type: map
    entry_schema: Any
    required: false
   'null':
    type: 'null'
    required: false