在下拉列表中添加空白行？

I have a php function that is returning a list of files from a folder (image files), I would like to know if it possible for me to get a "blank" entry added into the dropdown list (so I can "not select" something in the list), as well as the files it finds in the folder, here is the function.

<?php 

$folder = '../Pic/Upload'; 

echo '<select name="sabpic">'."
". 
     dropdown(image_filenames($folder), @$_POST['image']). 
     '</select>'."
".'</br></br>'; 

function image_filenames($dir) 
{ 
    $handle = @opendir($dir) 
        or die("I cannot open the directory '<b>$dir</b>' for reading."); 
    $images = array(); 
    while (false !== ($file = readdir($handle))) 
    { 
        if (eregi('\.(jpg|gif|png)$', $file)) 
        { 
            $images[] = $file; 
        } 
    } 
    closedir($handle); 
    return $images; 
} 

function dropdown($options_array, $selected = null) 
{ 
global $sabpicname;
    $return = null; 
    foreach($options_array as $option) 
    { 
        $return .= '<option value="'.$option.'"'. 
                   (($option == $sabpicname) ? ' selected="selected"' : null ). 
                   '>'.$option.'</option>'."
"; 
    } 
    return $return; 
} 

?>

So currently I would get a dropdown with

• Pic1.jpg
• Pic2.jpg

I would like to have

• "blank line"
• Pic1.jpg
• Pic2.jpg

Thanks for the help.

According to your code just replace $return = null; with $return = "<option></option>";

function dropdown($options_array, $selected = null) 
{ 
global $sabpicname;
    $return = "<option></option>"; 
    foreach($options_array as $option) 
    { 
        $return .= '<option value="'.$option.'"'. 
                   (($option == $sabpicname) ? ' selected="selected"' : null ). 
                   '>'.$option.'</option>'."
"; 
    } 
    return $return; 
} 

You can add the initial option like this ( I think ) that will initially dislay "Please Select" but is then no longer selectable after a choice has been made

function dropdown($options_array, $selected = null) { 
    global $sabpicname;
  $return = "<option disabled=true hidden='hidden'>Please Select";

  foreach($options_array as $option) { 
      $return .= '<option value="'.$option.'"'. 
                 (($option == $sabpicname) ? ' selected="selected"' : null ). 
                 '>'.$option.'</option>'."
"; 
  } 
  return $return; 
}