Not able to release postgres client using npm-postgres

Here is the code that I have tried.client.release() or client.end() is giving me UnhandledPromiseRejectionWarning .I would want to release the connection back to the pool or end it once data is inserted.

client.query(format(query, values), (err, res) => {
          if (err) {
            console.error(err, res);
            client.release();
          } else {
            console.log('POSTGRES DATA INSERTED SUCCESSFULLY');
            //  client.end();
            client.release();
          }
        });

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