title: Build a JSON_Object value in Flink SQL
body: <p>I have a Flink Table for which I want to write a select query that will return a JSON Object based on some fields.</p>
  <p>Here is the query I want to do (based on calcite syntax : <a href="https://calcite.apache.org/docs/reference.html#constructor-functions" rel="nofollow noreferrer">https://calcite.apache.org/docs/reference.html#constructor-functions</a>):</p>
  <pre><code>SELECT 
      myIdField,
      aFloatField,
      JSON_OBJECT('aFieldName':aFloatField)
  FROM myTable
  </code></pre>
  <p>But when I try to use this query with Flink, I get the following error :</p>
  <pre><code>org.apache.flink.table.api.ValidationException: SQL validation failed. No match found for function signature JSON_OBJECT(&lt;null&gt;, , )
  </code></pre>
  <p>What is the good way to do so ? I can't find anything about this in Flink documentation.</p>