Postgres always insert empty object `{}` for empty jsontext

[longquanzheng]

E.g. for commandRequest of nil in the below code:

It will insertert {} instead of NULL.
As a result

After upgrading to open API 7.1.0
( see https://github.com/OpenAPITools/openapi-generator/releases/tag/v7.1.0 for Go and OpenAPITools/openapi-generator#16863 )

There is a breaking change that it alwasy validate the required fields:

https://github.com/xcherryio/apis/blob/9ff80b8ba2c1bf8390f123e35707c63f56ef4d63/goapi/xcapi/model_command_request.go#L174

For now, we have to set the default value to emptyCommand and encodedObject

[longquanzheng]

cc @duoertai @zklgame