如果变量为0，则代码返回空字符串

每当容量为0时，我的PHP代码似乎只返回短语显示，而不是容量为0的房间。我该如何解决此问题？

$allowedFields = array(
    'Capacity',
    'Location',
    'RoomType'
);
// Retrieve only the allowed fields
$fields = array_intersect_key($_POST, array_flip($allowedFields));
// Remove whitespace
$fields = array_map('trim', $fields);
// Remove empty values
$fields = array_filter($fields);
// Filter values for HTML output
$fields = array_map('htmlentities', $fields);
// Create the variables
extract($fields, EXTR_SKIP);
{
$heading = 'Showing';
if(isset($RoomType)) {
    $heading .= ' ' . $RoomType;
}
if(isset($Capacity)) {
    $heading .= sprintf(' rooms with a capacity of %s', $Capacity);
}
if(isset($Location)) {
    $heading .= sprintf(' in %s Park', $Location);
}
}