Allow `null` for optional values.

I have implemented hierarchical outlining in my language server and vscode calls it on ctrl-shift-o, but it is never displaying it, only “No symbols found”. Log:

2018-08-26T15:23:40.449:app.d:processRequest:77 Calling provideDocumentSymbols
[Trace - 3:23:40 PM] Received response 'textDocument/documentSymbol - (24)' in 17ms.
Result: [
    {
        "children": [],
        "deprecated": false,
        "detail": null,
        "kind": 12,
        "name": "main",
        "range": {
            "end": {
                "character": 0,
                "line": 19
            },
            "start": {
                "character": 0,
                "line": 9
            }
        },
        "selectionRange": {
            "end": {
                "character": 0,
                "line": 9
            },
            "start": {
                "character": 0,
                "line": 9
            }
        }
    }
]

The outline panel is also not showing anything.

Version: "vscode-languageclient": "^5.0.1" (tsc complained about some issues in vscode failing to compile but I think this should be unaffected?), edit: fixed these by updating vscode engine to 1.26.0

[aeschli]

Makes sense to me to also allow ‘null’

[WebFreak001]

my server is implemented in D, where empty strings and arrays are equal to a null slice (0 length, null ptr), which is serialized by the json serializer I use by default to null. I have now added a custom serialization policy for the structs in question but I think it would be nice if the parser would be a bit more leniant on allowing null on values, especially because when using fixed data types in some languages it might not really be possible to define policies like ignoring unchanged values without a lot of hassle.