创建流程无默认值导致前端加载不出界面

[trdmm]

fix: flow_model has no default data when createFlow.

close #47.

[lthaoshao]

Turbo provides core process-driven capabilities that can be adapted to different front ends. Different front-end products may have different formats, and the default value set here is not compatible with all front-end products. Therefore, when the front-end is processing, it should be compatible with the form of null to ensure that it can be loaded normally, and the structure of the front-end itself can be saved when saving again.