fix(variables): accept JSON string and empty input for json_schema#165

WH-2099 merged 3 commits into

langgenius:mainlanggenius/graphon:mainfrom

shiyuanfang2nd:fix/variable-entity-json-schema-stringshiyuanfang2nd/graphon_mirror:fix/variable-entity-json-schema-stringCopy head branch name to clipboard