Fix build crash

pkg/analyzer/lib/src/generated/type_system.dart

Index: pkg/analyzer/lib/src/generated/type_system.dart
diff --git a/pkg/analyzer/lib/src/generated/type_system.dart b/pkg/analyzer/lib/src/generated/type_system.dart
index 35c0a888bfc09a8fe9bbbde73e5f002b7d0377bd..fb823260619f025fdc3ea6a5a279041f352537e6 100644
--- a/pkg/analyzer/lib/src/generated/type_system.dart
+++ b/pkg/analyzer/lib/src/generated/type_system.dart
@@ -811,7 +811,7 @@ class StrongTypeSystemImpl extends TypeSystem {
   /// Given a type return its name prepended with the URI to its containing
   /// library and separated by a comma.
   String _getTypeFullyQualifiedName(DartType type) {
-    return "${type?.element?.library?.source?.uri},$type";
+    return "${type?.element?.library?.identifier},$type";
   }
 
   /**