Unhandled Error!

Undefined index: HTTP_REFERER

Document	Cart
Document type	CMS page
Line	137
Exception class	Cms_ExecutionException

Code Highlight

							</table>
						</div>
					</div>
 
					<div class="box-footer">
						<div class="pull-left">
							<a href="<?php echo $_SERVER['HTTP_REFERER']; ?>" class="btn btn-small">
								<i class="icon-chevron-left"></i> &nbsp; Continue shopping
							</a>			
						</div>
 
						<div class="pull-right">
							<button type="submit" class="btn btn-small mm20 update-products" >

#	Document	Type
1	Cart	CMS page