@Override
        public void accept(SqlStatement stmt, String key) {
            stmt.define(key, null);
        }
<p>Define a {@code null} value, leaving the result up to the {@link org.jdbi.v3.core.statement.TemplateEngine} to decide.</p>
<p>
This value was specifically added to <a href="https://github.com/jdbi/jdbi/issues/1377">make conditionals work better with <code>StringTemplate</code></a>.
core/src/main/java/org/jdbi/v3/core/statement/EmptyHandling.java