Merge pull request #2609 from mmelvin0/master

Skip missing optional imports

lib/less/visitors/import-visitor.js

@@ -104,6 +104,7 @@ ImportVisitor.prototype = {
         var importVisitor = this,
             inlineCSS = importNode.options.inline,
             isPlugin = importNode.options.plugin,
+            isOptional = importNode.options.optional,
             duplicateImport = importedAtRoot || fullPath in importVisitor.recursionDetector;
 
         if (!context.importMultiple) {
@@ -120,6 +121,10 @@ ImportVisitor.prototype = {
             }
         }
 
+        if (!fullPath && isOptional) {
+            importNode.skip = true;
+        }
+
         if (root) {
             importNode.root = root;
             importNode.importedFilename = fullPath;