fix #339

lib/carto/tree/definition.js

@@ -97,6 +97,7 @@ tree.Definition.prototype.symbolizersToXML = function(env, symbolizers, zoom) {
     }
 
     sym_order = symbolizerList(sym_order);
+    var sym_count = 0;
 
     for (var i = 0; i < sym_order.length; i++) {
         var attributes = symbolizers[sym_order[i]];
@@ -105,6 +106,7 @@ tree.Definition.prototype.symbolizersToXML = function(env, symbolizers, zoom) {
         // Skip the magical * symbolizer which is used for universal properties
         // which are bubbled up to Style elements intead of Symbolizer elements.
         if (symbolizer === '*') continue;
+        sym_count++;
 
         var fail = tree.Reference.requiredProperties(symbolizer, attributes);
         if (fail) {
@@ -147,7 +149,7 @@ tree.Definition.prototype.symbolizersToXML = function(env, symbolizers, zoom) {
             }
         }
     }
-    if (!xml) return '';
+    if (!sym_count || !xml) return '';
     return '  <Rule>\n' + xml + '  </Rule>\n';
 };