Text box template variable isn't contained in the query

I publish a dashboard which uses simple-json-datasource v0.1.7(https://github.com/grafana/simple-json-datasource) through the Http API.

But the text box template variable isn’t contained in the query. Only when I change the value of the textbox and the time range to query again does the text box template variable appear in the query. I don’t know why.

Grafana Version 6.5.2 , CentOS7.