Fix a typo in the previous fix.

lib/source_map_stack_trace.dart

Index: lib/source_map_stack_trace.dart
diff --git a/lib/source_map_stack_trace.dart b/lib/source_map_stack_trace.dart
index 5d6664c5c3a096c6eb1a10cf2c4275c52b06af41..ae2f124d37219bde279cf5fb6d49e8ae8327627b 100644
--- a/lib/source_map_stack_trace.dart
+++ b/lib/source_map_stack_trace.dart
@@ -76,7 +76,7 @@ StackTrace mapStackTrace(Mapping sourceMap, StackTrace stackTrace,
           p.url.isWithin(packageResolver.packageRoot.toString(), sourceUrl)) {
         sourceUrl = "package:" + p.url.relative(sourceUrl,
             from: packageResolver.packageRoot.toString());
-      } else if (packageResolver.packageConfig != null) {
+      } else if (packageResolver.packageConfigMap != null) {
         for (var package in packageResolver.packageConfigMap.keys) {
           var packageUrl = packageResolver.packageConfigMap[package].toString();
           if (!p.url.isWithin(packageUrl, sourceUrl)) continue;