title: What format does a Google Data Studio DATE field expect from the connector?
body: <p>I am building a Google Data Studio connector with a field called <code>date</code>. The field's type is <code>YEAR_MONTH_DAY</code>. Now, when I return a string, for instance &quot;2020-09-22&quot;, the field shows <code>null</code> as a result. What value should my connector provide to have Data Studio recognize it as a date?</p>