Fix input-source-map-tracker for node@6.*

diff --git a/lib/utils/input-source-map-tracker.js b/lib/utils/input-source-map-tracker.js
index 7db9eb9..bfd9106 100644 (file)
--- a/lib/utils/input-source-map-tracker.js
+++ b/lib/utils/input-source-map-tracker.js
@@ -188,7 +188,7 @@ function trackContentSources(self, sourceFile) {
   consumer.sources.forEach(function (file, index) {
     var uniquePath = isRemote ?
       url.resolve(path.dirname(sourceFile), file) :
-      path.relative(self.relativeTo, path.resolve(path.dirname(sourceFile), file));
+      path.relative(self.relativeTo, path.resolve(path.dirname(sourceFile || '.'), file));
 
     sourcesMapping[uniquePath] = consumer.sourcesContent && consumer.sourcesContent[index];
   });