Execute find command through ssh2_exec in php & get results

Question

I am using php to execute a find command in linux for search a file in a directory and copy it into a other directory. My php code is :-

<?php
include 'config.php';
$mxf = $_POST['year'];
$year = substr($mxf, 0, 4);
$ndrive = $_POST['ndrive'];
$command = 'find /var/www/html/collections/'.$year.'/ -name ' . $mxf . ' -exec cp {} ' . $ndrive . ' \;';

$stream = ssh2_exec($con, $command);
stream_set_blocking($stream, true);
$stream_out = ssh2_fetch_stream($stream, SSH2_STREAM_STDIO);
echo stream_get_contents($stream_out);
ssh2_exec($con, 'logout');
?>

Now i want that script return false if requested file is not found in directory or file not available on server. So how can i handle this type of error with ssh2_exec command.