title: Pass NULL parameter to TFDConnection.ExecSQLScalar
body: <p>Is there a possibility to pass NULL value to some parameter of this FireDAC query?:</p>
  
  <pre><code>conn: TFDConnection;
  fPar1, fPar2, fPar3: OleVariant;
  
  cnt := conn.ExecSQLScalar(
      'SELECT COUNT(*) FROM my_table WHERE par1=:p1 AND par2=:p2 AND par3=:p3',
      [fPar1, fPar2, fPar3]
  );
  </code></pre>
  
  <p>Is it possible without intermediate <code>TFDQuery</code> using <code>TFDConnection</code> object only?</p>