Don't send not specified properties

E.g.

types.Completion('defaultdict')

will result in sending all other attributes along with label:

server-reply (id:21) Wed May 13 14:25:56 2020:
(:id 21 :jsonrpc "2.0" :result
     (:isIncomplete :json-false :items
		    [(:label "defaultdict" :kind nil :detail nil :documentation nil :deprecated :json-false :preselect :json-false :sortText nil :filterText nil :insertText nil :insertTextFormat nil :textEdit nil :additionalTextEdits nil :commitCharacters nil :command nil :data nil)]))

[pappasam]

@danixeee Another option is to have a library-specific value for an optionally undefined attribute:

UNDEFINED = object()

In the serializer, you can do an identity is check for UNDEFINED and not return it if the object is undefined:

def default_serializer(o):
    """JSON serializer for complex objects."""
    if isinstance(o, enum.Enum):
        return o.value
    d = {}
    for k, v in o.__dict__.items():
        if v is not UNDEFINED:
            d[k] = v
    return d

The above will still allow None to be placed into the dictionary.

I was drawn to this conversation by the following issue: https://github.com/pappasam/jedi-language-server/issues/38#issuecomment-675588654

Here’s a mypy-friendly way of achieving the above: https://www.python.org/dev/peps/pep-0484/#support-for-singleton-types-in-unions

[rwols]

There’s also a "range": null in the response to the textDocument/hover request. I’m guessing it’s the same underlying issue.

This library needs to distinguish between optional keys with typed values and mandatory keys.