null converted to []

[nickanthony-dgl]

JSON null values are not round-tripped. For example, this savejson(loadjson('{"myNullValue": null}')) results in:

ans =

    '{
     	"myNullValue":[]
     }
     '

The problem appears to be here: https://github.com/fangq/jsonlab/blob/cf573262eb12c1d1dc3668913c1f902e3452f566/loadjson.m#L560

[fangq]

matlab does not have a built-in data structure that is equivalent to null - the closest is [].

if you run matlab's built-in jsondecode function, it also maps null to '[]'

>> jsondecode('{"a":null}')

ans = 

  struct with fields:

    a: []

[nickanthony-dgl]

Yes, the problems I was running into with the built-in JSON functions are actually the reason I've started using JSONLab. Wouldn't it be possible to create a custom class to act as json null type?

[fangq]

here is my solution, committed as https://github.com/fangq/jsonlab/commit/747c99b5d434ce9f90097ddc0ad98bf1d5d45964

1. define an optional flag, for example, EmptyArrayAsNull, set to 0 by default, but can be enabled in your case
2. test that flag in this block inside matdata2json(), and return null if enabled.

this should give you what you want, i.e.

>> savejson('', loadjson('{"a":{},"b":[],"c":null}'), 'EmptyArrayAsNull',0, 'Compact', 1)

ans =

    '{"a":[],"b":[],"c":[]}'

>> savejson('', loadjson('{"a":{},"b":[],"c":null}'), 'EmptyArrayAsNull',1, 'Compact', 1)

ans =

    '{"a":null,"b":[],"c":null}'