be careful about a null url for data URLs

source-map-support.js

@@ -46,6 +46,7 @@ function retrieveFile(path) {
 // Support URLs relative to a directory, but be careful about a protocol prefix
 // in case we are in the browser (i.e. directories may start with "http://")
 function supportRelativeURL(file, url) {
+  if (!file) return url;
   var dir = path.dirname(file);
   var match = /^\w+:\/\/[^\/]*/.exec(dir);
   var protocol = match ? match[0] : '';
@@ -122,10 +123,8 @@ function mapSourcePosition(position) {
     // better to give a precise location in the compiled file than a vague
     // location in the original file.
     if (originalPosition.source !== null) {
-      if (sourceMap.url) {
       originalPosition.source = supportRelativeURL(
         sourceMap.url, originalPosition.source);
-      }
       return originalPosition;
     }
   }

test.js

@@ -241,6 +241,15 @@ it('throw with source map with gap', function() {
   ]);
 });
 
+it('sourcesContent with data URL', function() {
+  compareStackTrace(createMultiLineSourceMapWithSourcesContent(), [
+    'throw new Error("test");'
+  ], [
+    'Error: test',
+    /^    at Object\.exports\.test \(.*\/original.js:1001:5\)$/
+  ]);
+});
+
 it('default options', function(done) {
   compareStdout(done, createSingleLineSourceMap(), [
     '',