From 5a1f60b9257dd36ad0c0c2a114646c2bb7c72d07 Mon Sep 17 00:00:00 2001
From: Rolf Eike Beer <eike@sf-mail.de>
Date: Tue, 15 Mar 2016 22:39:42 +0100
Subject: [PATCH] do not render a bitmap when the vector tile contains no
 features

Simply hardlink the empty tile and serve that.
---
 bitmaptilerequest.js | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/bitmaptilerequest.js b/bitmaptilerequest.js
index 06cff3b..d6f94ec 100644
--- a/bitmaptilerequest.js
+++ b/bitmaptilerequest.js
@@ -169,8 +169,16 @@ BitmapTilerequest.prototype =
 								if (err)
 									self.tile.warn('Vector tile could not be saved.');
 
-								self.tile.debug('Rendering bitmap tile with style '+self.tile.style);
-								self.tile.render(renderCallback);
+								if (self.data.features.length === 0)
+								{
+									self.tile.debug('Vector tile without features, serving empty PNG tile for style ' + self.tile.style);
+									renderCallback(false, null);
+								}
+								else
+								{
+									self.tile.debug('Rendering bitmap tile with style ' + self.tile.style);
+									self.tile.render(renderCallback);
+								}
 							});
 						});
 					}