convert from version 2.3 to new（5.5），the output json lost frame event

[3tgame]

from the version 2.3 skeleton.json

{ "displayIndex": 4, "duration": 2, "event": "attack1", "transform": { "pX": 0, "pY": 0, "scX": 1, "scY": 1, "skX": 0, "skY": 0, "x": 43.3, "y": 3.35 }, "z": 4 }

after run the db2 -t new，search ‘event’ in the whole output json file， there is not event in the output skeleton.json file。
the version of this tool is dragonbones-tools@0.1.2